From 06fb5aceeb65a75b1cd643debd667c52fdcafcb9 Mon Sep 17 00:00:00 2001
From: Cliff Click <cliffc@acm.org>
Date: Sun, 8 Nov 2026 14:10:02 -0800
Subject: Better error messages

Better error messages.
Buffs to the std lib; getch() to fetch a single character; streaming I/O handles retries, and large sizes, with better error reporting.
Formatted strings.
Default int moved to i32.
TicTacToe, the game.
---
 chapter30/src/main/c/simple_crt.c                  | 124 ++++++++++++------
 .../com/seaofnodes/simple/codegen/BuildLRG.java    |   2 +-
 .../com/seaofnodes/simple/codegen/Coalesce.java    |   2 +-
 .../java/com/seaofnodes/simple/codegen/IFG.java    |   8 +-
 .../com/seaofnodes/simple/codegen/InstSelect.java  |   8 +-
 .../com/seaofnodes/simple/codegen/Machine.java     |  12 ++
 .../com/seaofnodes/simple/codegen/ParseAll.java    |  21 ++--
 .../com/seaofnodes/simple/codegen/RegAlloc.java    |  51 ++++++--
 .../com/seaofnodes/simple/codegen/SourceError.java |  16 ++-
 .../java/com/seaofnodes/simple/node/CallNode.java  |   2 +-
 .../com/seaofnodes/simple/node/FldOffNode.java     |   2 +-
 .../com/seaofnodes/simple/node/FormatNode.java     |  33 +++++
 .../java/com/seaofnodes/simple/node/LoadNode.java  |   3 +
 .../java/com/seaofnodes/simple/node/ScopeNode.java |   1 +
 .../seaofnodes/simple/node/cpus/arm/ExtendARM.java |  15 ++-
 .../com/seaofnodes/simple/node/cpus/arm/arm.java   |   3 +-
 .../simple/node/cpus/riscv/ExtendRISC.java         |  15 ++-
 .../seaofnodes/simple/node/cpus/riscv/riscv.java   |   3 +-
 .../simple/node/cpus/x86_64_v2/ExtendX86.java      |  15 ++-
 .../simple/node/cpus/x86_64_v2/x86_64_v2.java      |   4 +-
 .../com/seaofnodes/simple/parser/Allocations.java  |  20 +--
 .../com/seaofnodes/simple/parser/ControlFlow.java  |   4 +-
 .../com/seaofnodes/simple/parser/Declarations.java |  21 ++--
 .../com/seaofnodes/simple/parser/Expressions.java  |  41 ++++--
 .../com/seaofnodes/simple/parser/Functions.java    |  13 +-
 .../java/com/seaofnodes/simple/parser/Lexer.java   | 139 ++++++++++++++++-----
 .../java/com/seaofnodes/simple/parser/Parser.java  |  23 +++-
 .../com/seaofnodes/simple/parser/References.java   |  46 +++++--
 .../com/seaofnodes/simple/parser/Statements.java   |  27 ++--
 .../java/com/seaofnodes/simple/parser/Strings.java |  59 +++++++++
 .../java/com/seaofnodes/simple/parser/Structs.java |   6 +-
 .../java/com/seaofnodes/simple/parser/Types.java   |   6 +-
 .../com/seaofnodes/simple/type/TypeConAry.java     |  15 +++
 .../com/seaofnodes/simple/type/TypeConAryB.java    |   2 +-
 .../com/seaofnodes/simple/type/TypeInteger.java    |  10 +-
 chapter30/src/main/smp/sys.smp                     |   2 +
 chapter30/src/main/smp/sys/ary.smp                 |  26 +++-
 chapter30/src/main/smp/sys/aryi64.smp              |  25 ++--
 chapter30/src/main/smp/sys/aryu8.smp               |  45 +++----
 chapter30/src/main/smp/sys/io.smp                  |  75 +++++++----
 chapter30/src/main/smp/sys/libc.smp                |  25 +++-
 chapter30/src/main/smp/sys/rt.smp                  |   3 +
 chapter30/src/main/smp/sys/rt/simple_args.smp      |  22 ++++
 chapter30/src/main/smp/sys/text.smp                |  98 +++++++++++++++
 44 files changed, 838 insertions(+), 255 deletions(-)
 create mode 100644 chapter30/src/main/java/com/seaofnodes/simple/node/FormatNode.java
 create mode 100644 chapter30/src/main/java/com/seaofnodes/simple/parser/Strings.java
 create mode 100644 chapter30/src/main/smp/sys/rt.smp
 create mode 100644 chapter30/src/main/smp/sys/rt/simple_args.smp
 create mode 100644 chapter30/src/main/smp/sys/text.smp

(limited to 'chapter30/src/main')

diff --git a/chapter30/src/main/c/simple_crt.c b/chapter30/src/main/c/simple_crt.c
index 8656a3cc..438ae5f9 100644
--- a/chapter30/src/main/c/simple_crt.c
+++ b/chapter30/src/main/c/simple_crt.c
@@ -1,58 +1,106 @@
 #include <stdint.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <errno.h>
+#include <termios.h>
+#include <unistd.h>
 
 // errno may be thread-local or a macro calling a platform accessor.
 int32_t simple_errno(void) { return errno; }
+int32_t simple_set_errno(int32_t error) { errno = error; return -1; }
+// Export platform errno constants; the buffering and retry loops are Simple.
+// C identifiers avoid the macros; linker names match the Simple bindings.
+int32_t simple_EINTR __asm__("EINTR") = EINTR;
+int32_t simple_EIO __asm__("EIO") = EIO;
+int32_t simple_EINVAL __asm__("EINVAL") = EINVAL;
+int32_t simple_EOVERFLOW __asm__("EOVERFLOW") = EOVERFLOW;
 
-// Native process arguments converted to ordinary Simple array layouts.
-// The outer array is mutable; every contained byte array is published as
-// immutable and non-null to Simple code.
+// Read one stdin byte, without terminal line editing or echo. POSIX terminals
+// include Cygwin consoles; redirected files/pipes need no mode change.
+// Return 0..255, or -1 with errno set to EOF or an OS error. Control characters,
+// including Ctrl-C, are returned as bytes so the mode is restored first.
+int32_t simple_getch(void) {
+    struct termios saved, mode;
+    int terminal = tcgetattr(STDIN_FILENO, &saved) == 0;
+    if (!terminal && errno != ENOTTY)
+        return -1;
+    if (terminal) {
+        mode = saved;
+        mode.c_lflag &= ~(ICANON | ECHO | ECHONL | ISIG | IEXTEN);
+        mode.c_iflag &= ~IXON;
+        mode.c_cc[VMIN] = 1;
+        mode.c_cc[VTIME] = 0;
+        if (tcsetattr(STDIN_FILENO, TCSANOW, &mode) != 0)
+            return -1;
+    }
+    unsigned char byte;
+    ssize_t count = read(STDIN_FILENO, &byte, 1);
+    int read_errno = errno;
+    if (terminal) {
+        int restored;
+        do {
+            restored = tcsetattr(STDIN_FILENO, TCSANOW, &saved);
+        } while (restored != 0 && errno == EINTR);
+        if (restored != 0)
+            return -1;
+    }
+    if (count < 0) {
+        errno = read_errno;
+        return -1;
+    }
+    if (count == 0) {
+        errno = EOF;
+        return -1;
+    }
+    return byte;
+}
+
+// Simple byte-array layout, used only by the floating-point formatter.
 typedef struct SimpleBytes {
     uint32_t len;
     unsigned char bytes[];
 } SimpleBytes;
 
-typedef struct SimpleArgs {
-    uint32_t len;
-    uint32_t pad;
-    SimpleBytes *args[];
-} SimpleArgs;
+// Binary floating-point conversion is the only native formatting primitive.
+// Buffering, integer conversion, string precision and padding live in sys.text.
+SimpleBytes *simple_text_float(double value, int64_t spec,
+                               int64_t width, int64_t precision) {
+    char kind = spec & 255;
+    if (!kind) { kind = 'g'; precision = 17; }
+    if (!strchr("fFeEgGaA", kind) || (spec & ~8191LL) ||
+        width < 0 || width > INT32_MAX || precision < -1 || precision > INT32_MAX)
+        abort();
+    char fmt[64], *p = fmt;
+    *p++ = '%';
+    const char *flags = "-+ #0";
+    for (int i=0; i<5; i++) if (spec & (256LL<<i)) *p++ = flags[i];
+    if (width) p += sprintf(p, "%d", (int)width);
+    if (precision >= 0) p += sprintf(p, ".%d", (int)precision);
+    *p++ = kind;
+    *p = 0;
+    int len = snprintf(NULL, 0, fmt, value);
+    if (len < 0) abort();
+    SimpleBytes *str = malloc(sizeof(*str) + (size_t)len + 1);
+    if (!str) abort();
+    str->len = (uint32_t)len;
+    snprintf((char *)str->bytes, (size_t)len + 1, fmt, value);
+    return str;
+}
+// Simple does not yet dereference raw native pointers. Keep just the argv
+// element access here; allocation and array construction live in sys/rt/simple_args.smp.
+const char *simple_argv(char **argv, int64_t index) {
+    return argv[index];
+}
 
 __attribute__((CALL_CONV))
-extern int64_t simple_main(SimpleArgs *args);
-
-static SimpleArgs *simple_args(int argc, char **argv) {
-    if (argc < 0 || (uint64_t)argc > UINT32_MAX)
-        return NULL;
-
-    SimpleArgs *args = calloc(1, sizeof(*args) + (size_t)argc * sizeof(args->args[0]));
-    if (args == NULL)
-        return NULL;
-    args->len = (uint32_t)argc;
-
-    for (int i = 0; i < argc; i++) {
-        size_t len = strlen(argv[i]);
-        if (len > UINT32_MAX) {
-            free(args);
-            return NULL;
-        }
-        SimpleBytes *str = malloc(sizeof(*str) + len);
-        if (str == NULL) {
-            for (int j = 0; j < i; j++) free(args->args[j]);
-            free(args);
-            return NULL;
-        }
-        str->len = (uint32_t)len;
-        memcpy(str->bytes, argv[i], len);
-        args->args[i] = str;
-    }
-    return args;
-}
+extern void *simple_args(int64_t argc, char **argv);
+__attribute__((CALL_CONV))
+extern int64_t simple_main(void *args);
 
 int main(int argc, char **argv) {
-    SimpleArgs *args = simple_args(argc, argv);
+    // simple_args fills every slot before publishing this as u8[~][].
+    void *args = simple_args(argc, argv);
     if (args == NULL)
         return 1;
     // The language-level hidden receiver is not part of the emitted ABI for
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/codegen/BuildLRG.java b/chapter30/src/main/java/com/seaofnodes/simple/codegen/BuildLRG.java
index 0b314978..8d0237ea 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/codegen/BuildLRG.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/codegen/BuildLRG.java
@@ -16,7 +16,7 @@ abstract public class BuildLRG {
     // true if no hard-conflicts, although we still might not color.
     public static boolean run(int round, RegAlloc alloc) {
         FunNode fun = null;
-        for( Node bb : alloc._code._cfg ) {
+        for( Node bb : alloc._cfg ) {
             if( bb instanceof FunNode fun2 )
                 fun = fun2;
             for( Node n : bb.outs() ) {
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/codegen/Coalesce.java b/chapter30/src/main/java/com/seaofnodes/simple/codegen/Coalesce.java
index 689ceceb..dbde2f8b 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/codegen/Coalesce.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/codegen/Coalesce.java
@@ -13,7 +13,7 @@ abstract public class Coalesce {
 
         // Walk all the splits, looking for coalesce chances
         boolean progress = false;
-        for( CFGNode bb : alloc._code._cfg ) {
+        for( CFGNode bb : alloc._cfg ) {
             outer:
             for( int j=0; j<bb.nOuts(); j++ ) {
                 Node n = bb.out(j);
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/codegen/IFG.java b/chapter30/src/main/java/com/seaofnodes/simple/codegen/IFG.java
index d15e66da..6ad7c0ad 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/codegen/IFG.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/codegen/IFG.java
@@ -72,7 +72,7 @@ abstract public class IFG {
         WORK.clear();
 
         // Last block has nothing live out
-        for( CFGNode bb : alloc._code._cfg )
+        for( CFGNode bb : alloc._cfg )
             if( bb.blockHead())
                 WORK.push( bb );
 
@@ -164,6 +164,10 @@ abstract public class IFG {
         // Also record use-side spills for biased coloring.
         // Then make all inputs live.
         for( int i=1; i<n.nIns(); i++ ) {
+            // Metadata and scheduling dependencies do not consume registers.
+            // In particular, a static call's hidden class argument has no ABI
+            // location and must not keep its constant live across other calls.
+            if( ((MachNode)n).regmap(i)==null ) continue;
             Node def = n.in(i);
             if( def==null ) continue;
             LRG lrg1 = alloc.lrg(def);
@@ -480,7 +484,7 @@ abstract public class IFG {
 
     private static int functionArea(FunNode fun, RegAlloc alloc) {
         int area=0;
-        for( CFGNode bb : alloc._code._cfg )
+        for( CFGNode bb : alloc._cfg )
             if( bb.fun()==fun )
                 area += bb.nOuts();
         return area;
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/codegen/InstSelect.java b/chapter30/src/main/java/com/seaofnodes/simple/codegen/InstSelect.java
index 5fc002a1..2595b4ad 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/codegen/InstSelect.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/codegen/InstSelect.java
@@ -85,13 +85,7 @@ class InstSelect {
         }
 
         // Produce a machine node from n; map it to flag as done so stops cycles.
-        if( n instanceof MemOpNode mem && mem.off() instanceof ExternOffsetNode off ) {
-            // External fields replace base+offset with symbol+0. Keep the ideal
-            // declaring type on the address for machine load/store width selection.
-            TypeMemPtr ptr = (TypeMemPtr)mem.ptr()._type;
-            n._inputs.set(2,new ExternNode(TypeMemPtr.make((byte)2,ptr._obj,true),off._extern));
-            n._inputs.set(3,ConstantNode.raw(TypeInteger.ZERO));
-        }
+        if( n instanceof MemOpNode mem ) Machine.externalAddress(mem);
         map.put(n, x=_code._mach.instSelect(n) );
         // Carry loop-tree and pre-order info across the ideal->mach transition
         if( n instanceof CFGNode ncfg && x instanceof CFGNode xcfg ) {
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/codegen/Machine.java b/chapter30/src/main/java/com/seaofnodes/simple/codegen/Machine.java
index 3eee8fc3..6ccf6b19 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/codegen/Machine.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/codegen/Machine.java
@@ -3,6 +3,7 @@ package com.seaofnodes.simple.codegen;
 import com.seaofnodes.simple.node.*;
 import com.seaofnodes.simple.type.TypeFunPtr;
 import com.seaofnodes.simple.type.TypeInteger;
+import com.seaofnodes.simple.type.TypeMemPtr;
 
 abstract public class Machine {
     // Human readable machine name.  Something like "x86-64" or "arm" or "risc5"
@@ -46,6 +47,17 @@ abstract public class Machine {
     // Instruction select from ideal nodes
     public abstract Node instSelect( Node n );
 
+    // Lower external fields before selecting a memory operation, including
+    // loads absorbed into another instruction rather than selected separately.
+    public static void externalAddress(MemOpNode mem) {
+        if( mem.off() instanceof ExternOffsetNode off ) {
+            // Retain the declaring type for load/store width selection.
+            TypeMemPtr ptr = (TypeMemPtr)mem.ptr()._type;
+            mem._inputs.set(2,new ExternNode(TypeMemPtr.make((byte)2,ptr._obj,true),off._extern));
+            mem._inputs.set(3,ConstantNode.raw(TypeInteger.ZERO));
+        }
+    }
+
     /** Stack Slot Numbering
 
 RA gives all registers a number, starting at 0.  Stack slots continue this
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/codegen/ParseAll.java b/chapter30/src/main/java/com/seaofnodes/simple/codegen/ParseAll.java
index 5f8a0ec0..3306ff8f 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/codegen/ParseAll.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/codegen/ParseAll.java
@@ -140,7 +140,7 @@ public abstract class ParseAll {
                     fref._name = TypeStruct.addClzPrefix(xcunit._cname);
                     cunit.addDep(xcunit);
                 } else {
-                    throw new RuntimeException("Undefined name '" + fref._name +"'");
+                    throw fref.err();
                 }
             } catch( IOException ioe ) {
                 throw new RuntimeException(ioe);
@@ -297,14 +297,6 @@ public abstract class ParseAll {
             Parser.TYPES.put(cunit._cname,ptr._obj);
     }
 
-    // Symbol not found in source code (or we would not be here).
-    // Search the module for the fref
-    public static CompUnit findCompUnitOrThrow(CodeGen code, CompUnit cu, String symbol) {
-        CompUnit cu2 =  findCompUnit(code,cu,symbol);
-        if( cu2 != null ) return cu2;
-        throw new RuntimeException("Undefined name '" + symbol +"'");
-    }
-
     public static CompUnit findCompUnit(CodeGen code, CompUnit cu, String symbol) {
         // Symbol not found in source code (or we would not be here).
         // Search the module for the fref
@@ -328,8 +320,15 @@ public abstract class ParseAll {
     // However if A/B contains "Y", the search would be for A.B.Y then A.Y both of
     // which do not exist.
     private static CompUnit findCUnitModule( CodeGen code, CompUnit cunit, String symbol ) throws IOException {
-        if( cunit == null )     // Ran off top of module scope?
-            return null;        // Failed search
+        if( cunit == null ) {
+            // The module root is also a namespace. In particular, a root
+            // client can resolve sys.text from source, without installed .o's.
+            String fname=symbol.replace('.','/');
+            if( !new File(code._modDir+"/"+fname+".smp").exists() ) return null;
+            CompUnit root=makeCUnit(code,null,fname);
+            if( root._clz==null && WORK.find(root)==-1 ) enqueue(root);
+            return root;
+        }
 
         // Check self
         if( cunit._name.equals(symbol) )
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java b/chapter30/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
index f1aa18ef..3991cd48 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
@@ -54,6 +54,8 @@ public class RegAlloc {
 
     // Top-level program graph structure
     final CodeGen _code;
+    // Scheduled blocks of the function currently being allocated.
+    Ary<CFGNode> _cfg;
 
     public int _spills, _spillScaled;
 
@@ -161,7 +163,7 @@ public class RegAlloc {
     }
 
     // -----------------------
-    RegAlloc( CodeGen code ) { _code = code; }
+    RegAlloc( CodeGen code ) { _code = code; _cfg = code._cfg; }
 
     public void regAlloc() {
         // Insert callee-save registers
@@ -186,18 +188,41 @@ public class RegAlloc {
         // Expensive assert: useful when chasing cross-function allocator edges.
         //assert verifyFunctionLocalEdges();
 
-        // Top driver: repeated rounds of coloring and splitting.
-        byte round=0;
-        while( !graphColor(round) ) {
-            split(round);
-            if( round >= 7 )    // Really expect to be done soon
-                throw new IllegalStateException("Register allocation made no progress after eight rounds");
-            round++;
+        // Each function owns its retry budget. Keep completed assignments while
+        // reusing the live-range and interference scratch space for the next.
+        IdentityHashMap<Node,LRG> colored = new IdentityHashMap<>();
+        _cfg = new Ary<>(CFGNode.class);
+        for( CFGNode bb : _code._cfg ) {
+            if( bb instanceof FunNode && !_cfg.isEmpty() ) {
+                allocateFunction();
+                colored.putAll(_lrgs);
+                _cfg.clear();
+            }
+            _cfg.add(bb);
         }
+        if( !_cfg.isEmpty() ) {
+            allocateFunction();
+            colored.putAll(_lrgs);
+        }
+        _lrgs.clear();
+        _lrgs.putAll(colored);
+        _cfg = _code._cfg;
         postColor();                       // Remove no-op spills
         _done = true;
     }
 
+    private void allocateFunction() {
+        _deferredLoopSelf.clear();
+        for( byte round=0; !graphColor(round); round++ ) {
+            split(round);
+            if( round >= 7 ) {
+                FunNode fun = _cfg.at(0).fun();
+                throw new IllegalStateException("Register allocation failed after eight rounds in "+
+                                                (fun==null ? "<root>" : fun.label()));
+            }
+        }
+    }
+
     boolean verifyFunctionLocalEdges() {
         for( CFGNode bb : _code._cfg )
             for( Node use : bb._outputs ) {
@@ -477,7 +502,10 @@ public class RegAlloc {
                         split.killOrdered();
                 }
                 for( int i=1; i<(deferred.containsKey(phi) ? 2 : phi.nIns()); i++ )
-                    if( i==1 || sharedPhiInput(phi,i) )
+                    // Backedges may be joined indirectly through two-address
+                    // chains, even when their input nodes are distinct. After
+                    // the cold-only attempt, isolate those inputs as well.
+                    if( i==1 || phi.region() instanceof LoopNode || sharedPhiInput(phi,i) )
                         insertBefore(phi,i,"use/self/phi",round,lrg);
             }
             // Split before two-address ops which extend the live range
@@ -653,9 +681,8 @@ public class RegAlloc {
                 return;
         }
         makeSplit(def,kind,round,lrg,umask).insertBefore(n, i);
-        // Skip split-of-split same block
-        if( skip && def instanceof SplitNode && cfg==def.cfg0() )
-            n.in(i).setDefOrdered(1,def.in(1));
+        // Keep the def-side transfer: a kill between the two copies may be
+        // exactly why this range split. Coalescing can join them when safe.
     }
     void insertBefore(Node n, int i, String kind, byte round, LRG lrg) {
         insertBefore(n,i,kind,round,lrg,true);
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/codegen/SourceError.java b/chapter30/src/main/java/com/seaofnodes/simple/codegen/SourceError.java
index f2f46146..5be0585f 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/codegen/SourceError.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/codegen/SourceError.java
@@ -16,6 +16,10 @@ public abstract class SourceError {
             source=cu._src!=null ? cu._src.getBytes(StandardCharsets.UTF_8)
                 : file==null ? null : Files.readAllBytes(Path.of(file));
         } catch( IOException ex ) { source=null; }
+        return format(name,source,pos,message);
+    }
+
+    public static String format(String name, byte[] source, int pos, String message) {
         if( source==null || pos<0 || pos>source.length )
             return name+": error: "+message+" (source unavailable at byte offset "+pos+")";
 
@@ -28,22 +32,24 @@ public abstract class SourceError {
         int point=Math.min(pos,end);
         String before=new String(source,start,point-start,StandardCharsets.UTF_8);
         String text=new String(source,start,end-start,StandardCharsets.UTF_8);
-        int column=before.codePointCount(0,before.length())+1;
-        SB sb=new SB().p(name).p(':').p(line).p(':').p(column).p(": error: ").p(message).p("\n    ");
+        SB excerpt=new SB();
         int width=0, caret=0;
         for( int i=0; i<text.length(); ) {
             if( i==before.length() ) caret=width;
             int ch=text.codePointAt(i);
             if( ch=='\t' ) {
                 int spaces=8-(width%8);
-                for( int j=0; j<spaces; j++ ) sb.p(' ');
+                for( int j=0; j<spaces; j++ ) excerpt.p(' ');
                 width+=spaces;
-            } else { sb.p(new String(Character.toChars(ch))); width++; }
+            } else { excerpt.p(new String(Character.toChars(ch))); width++; }
             i+=Character.charCount(ch);
         }
         if( before.length()==text.length() ) caret=width;
+        // Emacs compilation mode defaults to display columns, with 8-column tabs.
+        SB sb=new SB().p(name).p(':').p(line).p(':').p(caret+1).p(": error: ").p(message)
+            .p("\n    ").p(excerpt.toString());
         sb.p("\n    ");
-        for( int i=0; i<caret; i++ ) sb.p('-');
+        for( int i=0; i<caret; i++ ) sb.p('_');
         return sb.p('^').toString();
     }
 }
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/node/CallNode.java b/chapter30/src/main/java/com/seaofnodes/simple/node/CallNode.java
index 91d27330..ac5e4eee 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/node/CallNode.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/node/CallNode.java
@@ -242,7 +242,7 @@ public class CallNode extends CFGNode {
         if( !tfp.notNull() )
             return Parser.error( "Might be null calling "+tfp, _loc);
         if( nargs() != tfp.nargs() )
-            return Parser.error( "Expecting "+tfp.nargs()+" arguments, but found "+nargs(), _loc);
+            return Parser.error( "Expecting "+(tfp.nargs()-1)+" arguments, but found "+(nargs()-1), _loc);
 
         // Check for args
         for( int i=0; i<tfp.nargs(); i++ )
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/node/FldOffNode.java b/chapter30/src/main/java/com/seaofnodes/simple/node/FldOffNode.java
index 09e5eac8..e49162f4 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/node/FldOffNode.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/node/FldOffNode.java
@@ -49,7 +49,7 @@ public class FldOffNode extends TypeNode {
 
     @Override public Parser.ParseException err() {
         if( in(1)._type instanceof TypeMemPtr tmp && tmp._obj._fref )
-            return Parser.error("Unknown struct type '"+tmp._obj._name+"'",null);
+            return Parser.error("Unknown struct type '"+tmp._obj._name+"'",_loc);
         return null;
     }
 }
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/node/FormatNode.java b/chapter30/src/main/java/com/seaofnodes/simple/node/FormatNode.java
new file mode 100644
index 00000000..d34b342d
--- /dev/null
+++ b/chapter30/src/main/java/com/seaofnodes/simple/node/FormatNode.java
@@ -0,0 +1,33 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.parser.Lexer;
+import com.seaofnodes.simple.parser.Parser;
+import com.seaofnodes.simple.type.*;
+
+/** Resolve default formatting through normal type flow, including forward
+ * references. Valid programs fold this selector before serialization/codegen. */
+public final class FormatNode extends Node {
+    private final Lexer _site;
+    public FormatNode(Node value, Node ints, Node floats, Node strings, Lexer site) {
+        super(null,value,ints,floats,strings);
+        _site=site;
+    }
+    @Override public String label() { return "Format"; }
+    private int choice() {
+        Type t=in(1)._type;
+        if( t instanceof TypeInteger ) return 2;
+        if( t instanceof TypeFloat ) return 3;
+        if( t instanceof TypeMemPtr p && !p.nullable() && p._obj.isAry() &&
+            p._obj._name.equals("[]u8") ) return 4;
+        return 0;
+    }
+    @Override public Type compute() {
+        if( in(1)._type.isHigh() ) return Type.TOP;
+        int c=choice();
+        return c==0 ? in(2)._type.meet(in(3)._type).meet(in(4)._type) : in(c)._type;
+    }
+    @Override public Node idealize() { int c=choice(); return c==0 ? null : in(c); }
+    @Override public Parser.ParseException err() {
+        return Parser.error("Cannot format "+in(1)._type+"; expected an integer, float, or byte string",_site);
+    }
+}
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/node/LoadNode.java b/chapter30/src/main/java/com/seaofnodes/simple/node/LoadNode.java
index 85ab29f9..eb78ed1f 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/node/LoadNode.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/node/LoadNode.java
@@ -395,6 +395,9 @@ public class LoadNode extends MemOpNode {
     // load will need to zero/sign-extend.
     private Node extend(Node val) {
         if( !(declaredType() instanceof TypeInteger ti) ) return val;
+        // A typed load can already know its width while the stored value is
+        // still unresolved. Do not replace it with an untyped shift/and chain.
+        if( !(val._type instanceof TypeInteger) ) { addDep(val); return null; }
         if( ti._min==0 )        // Unsigned
             return new AndNode(null,val,con(ti._max));
         // Signed extension
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/node/ScopeNode.java b/chapter30/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
index 1130cf44..80d2aa0a 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
@@ -638,6 +638,7 @@ public class ScopeNode extends MemMergeNode {
         int i = _guards._len;
         while( i > 0 ) {
             Node  cast = _guards.at(--i);
+            if( cast instanceof FunNode ) break; // Function boundary
             if( cast instanceof CFGNode ) continue; // Marker between guard sets
             Node xpred = _guards.at(--i);
             if( xpred == pred )
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/arm/ExtendARM.java b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/arm/ExtendARM.java
index 814a82c2..da9afe71 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/arm/ExtendARM.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/arm/ExtendARM.java
@@ -6,14 +6,21 @@ import com.seaofnodes.simple.node.*;
 import com.seaofnodes.simple.type.TypeInteger;
 import com.seaofnodes.simple.util.SB;
 
-// Convert a narrow C return register to Simple's full-width integer value.
+// Normalize narrow parameters and C return values to full-width integers.
 public class ExtendARM extends MachConcreteNode {
     final int _bits;
     final boolean _signed;
     ExtendARM(ProjNode prj, TypeInteger ret) {
-        super(prj);
-        _inputs.set(0,null);
-        _inputs.add(new ProjARM(prj));
+        this(prj,new ProjARM(prj),ret);
+    }
+    ExtendARM(ParmNode parm, TypeInteger decl) {
+        this(parm,new ParmARM(parm),decl);
+    }
+    private ExtendARM(Node ideal, Node value, TypeInteger ret) {
+        super(ideal);
+        _inputs.clear();
+        _inputs.add(null);
+        _inputs.add(value);
         _bits = 8 << ret.log_size();
         _signed = ret._min < 0;
     }
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
index 3c965da5..ee7b0fc3 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
@@ -332,7 +332,8 @@ public class arm extends Machine {
         case NewNode nnn     -> new NewARM(nnn);
         case NotNode not     -> new NotARM(not);
         case OrNode or       -> or(or);
-        case ParmNode parm   -> new ParmARM(parm);
+        case ParmNode parm   -> parm._declaredType instanceof TypeInteger ti && ti.log_size()<3
+            ? new ExtendARM(parm,ti) : new ParmARM(parm);
         case BulkMemPhiNode phi -> new BulkMemPhiNode(phi);
         case MemPhiNode phi  -> new MemPhiNode(phi);
         case PhiNode phi     -> new PhiNode(phi);
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/riscv/ExtendRISC.java b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/riscv/ExtendRISC.java
index 5bd3ec1c..11182133 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/riscv/ExtendRISC.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/riscv/ExtendRISC.java
@@ -6,14 +6,21 @@ import com.seaofnodes.simple.node.*;
 import com.seaofnodes.simple.type.TypeInteger;
 import com.seaofnodes.simple.util.SB;
 
-// Convert a narrow C return register to Simple's full-width integer value.
+// Normalize narrow parameters and C return values to full-width integers.
 public class ExtendRISC extends MachConcreteNode {
     final int _bits;
     final boolean _signed;
     ExtendRISC(ProjNode prj, TypeInteger ret) {
-        super(prj);
-        _inputs.set(0,null);
-        _inputs.add(new ProjRISC(prj));
+        this(prj,new ProjRISC(prj),ret);
+    }
+    ExtendRISC(ParmNode parm, TypeInteger decl) {
+        this(parm,new ParmRISC(parm),decl);
+    }
+    private ExtendRISC(Node ideal, Node value, TypeInteger ret) {
+        super(ideal);
+        _inputs.clear();
+        _inputs.add(null);
+        _inputs.add(value);
         _bits = 8 << ret.log_size();
         _signed = ret._min < 0;
     }
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java
index 0195542c..378955a5 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java
@@ -236,7 +236,8 @@ public class riscv extends Machine {
         case NewNode      nnn -> nnn(nnn);
         case NotNode      not -> new NotRISC(not);
         case OrNode        or -> or(or);
-        case ParmNode    parm -> new ParmRISC(parm);
+        case ParmNode    parm -> parm._declaredType instanceof TypeInteger ti && ti.log_size()<3
+            ? new ExtendRISC(parm,ti) : new ParmRISC(parm);
         case BulkMemPhiNode phi-> new BulkMemPhiNode(phi);
         case MemPhiNode  phi  -> new MemPhiNode(phi);
         case PhiNode      phi -> new PhiNode(phi);
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ExtendX86.java b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ExtendX86.java
index 1a6ae123..9f4da6b8 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ExtendX86.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ExtendX86.java
@@ -6,14 +6,21 @@ import com.seaofnodes.simple.node.*;
 import com.seaofnodes.simple.type.TypeInteger;
 import com.seaofnodes.simple.util.SB;
 
-// Convert a narrow C return register to Simple's full-width integer value.
+// Normalize narrow parameters and C return values to full-width integers.
 public class ExtendX86 extends MachConcreteNode {
     final int _bits;
     final boolean _signed;
     ExtendX86(ProjNode prj, TypeInteger ret) {
-        super(prj);
-        _inputs.set(0,null);
-        _inputs.add(new ProjX86(prj));
+        this(prj,new ProjX86(prj),ret);
+    }
+    ExtendX86(ParmNode parm, TypeInteger decl) {
+        this(parm,new ParmX86(parm),decl);
+    }
+    private ExtendX86(Node ideal, Node value, TypeInteger ret) {
+        super(ideal);
+        _inputs.clear();
+        _inputs.add(null);
+        _inputs.add(value);
         _bits = 8 << ret.log_size();
         _signed = ret._min < 0;
     }
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
index 3dc93bf6..3d71b4ea 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
@@ -306,7 +306,8 @@ public class x86_64_v2 extends Machine {
         case NewNode      nnn -> new NewX86(nnn);
         case NotNode      not -> new NotX86(not);
         case OrNode        or -> or(or);
-        case ParmNode    parm -> new ParmX86(parm);
+        case ParmNode    parm -> parm._declaredType instanceof TypeInteger ti && ti.log_size()<3
+            ? new ExtendX86(parm,ti) : new ParmX86(parm);
         case BulkMemPhiNode phi-> new BulkMemPhiNode(phi);
         case MemPhiNode  phi  -> new MemPhiNode(phi);
         case PhiNode      phi -> new PhiNode(phi);
@@ -555,6 +556,7 @@ public class x86_64_v2 extends Machine {
     private static int off, scale, imm;
     private static Node idx, val;
     private <N extends MemOpNode > N address(N mop) {
+        externalAddress(mop);
         off = scale = imm = 0;  // Reset
         idx = val = null;
         Node base = mop.ptr();
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/Allocations.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/Allocations.java
index be68e10e..861f95b6 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/parser/Allocations.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/Allocations.java
@@ -14,28 +14,30 @@ final class Allocations {
        Parse an allocation
      */
     Node parseNew() {
+        P._lexer.skipWhiteSpace();
+        Lexer site=P.loc();
         Type t = P.types.parseType();
         if( t==null ) {
             String tname = P._lexer.matchId();
             if( tname==null || Parser.KEYWORDS.contains(tname) )
-                throw P.error("Expected a type");
+                throw Parser.error("Expected a type after 'new'",site);
             t = P.types.forwardRefType(tname);
         }
         // Parse ary[ length_expr ]
         if( P.match("[") ) {
             if( !t.makeZero().isa(t) )
-                throw P.error("Cannot allocate a non-nullable, since arrays are always zero/null filled");
+                throw Parser.error("Cannot allocate a non-nullable, since arrays are always zero/null filled",site);
             Node len = P.expressions.parseAssignment().keep();
             P.require("]");
             return allocArray(P.types.typeAry(t,false),len);
         } else {
             if( !(t instanceof TypeMemPtr tmp) )
-                throw P.error("Cannot allocate a "+t.str());
-            return allocStruct(tmp._obj);
+                throw Parser.error("Cannot allocate a "+t.str(),site);
+            return allocStruct(tmp._obj,site);
         }
     }
 
-    private Node allocStruct(TypeStruct ts) {
+    private Node allocStruct(TypeStruct ts, Lexer site) {
         Ary<Node> ctorArgs = constructorArgs();
         // A field declaration can leave a short forward type name in TYPES.
         // Allocation happens in lexical context, so resolve that short name
@@ -45,7 +47,7 @@ final class Allocations {
         if( resolved instanceof TypeStruct rts ) ts = rts;
         TypeStruct clz = (TypeStruct)Parser.TYPES.get(TypeStruct.addClzPrefix(typeName));
         if( clz==null )
-            throw P.error("Unknown struct type '" + ts._name + "'");
+            throw Parser.error("Unknown struct type '" + ts._name + "'",site);
         Field afld = clz.field("<new>");
         Node alloc;
         if( afld != null ) {
@@ -56,7 +58,7 @@ final class Allocations {
                 : new FunPtrNode(tfp,P._code._start,fun.ret()).peephole();
         } else {
             if( !ts._fref )
-                throw P.error("Constructor arguments for '" + ts._name + "' but no constructor is defined");
+                throw Parser.error("Constructor arguments for '" + ts._name + "' but no constructor is defined",site);
             Type[] sig = new Type[ctorArgs._len];
             for( int i = 0; i<ctorArgs._len; i++ )
                 sig[i] = ctorArgs.at(i)._type;
@@ -111,12 +113,12 @@ final class Allocations {
         return self.unkeep();
     }
 
-    Node newString(String s) {
+    Node newString(byte[] s) {
         TypeStruct ts = P.types.typeAry(TypeInteger.U8,true);
         int  lenAlias = ts.field("#" )._alias;
         int elemAlias = ts.field("[]")._alias;
         TypeConAryB body = TypeConAryB.make(s);
-        TypeInteger slen = TypeInteger.constant(s.length());
+        TypeInteger slen = TypeInteger.constant(s.length);
         // Make a TMP, not-null (byte)2, singleton (true) (requires text
         // strings are hash-interned), with a TypeStruct having a constant
         // array body.
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/ControlFlow.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/ControlFlow.java
index caa73076..6c626669 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/parser/ControlFlow.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/ControlFlow.java
@@ -14,6 +14,8 @@ final class ControlFlow {
 
     // Parse a conditional expression, merging results.
     Node conditional( Node pred, String fside ) {
+        Lexer site=P.loc();
+        if( !fside.equals("else") ) site._position-=fside.equals(":") ? 1 : 2;
         // IfNode takes current control and predicate
         pred.keep();
         Node ifNode = new IfNode(P.ctrl(), pred).peephole();
@@ -88,7 +90,7 @@ final class ControlFlow {
         Node ret = P.peep(new PhiNode("",r,lhs.unkeep(),rhs.unkeep()));
         // Immediately fail e.g. `arg ? 7 : ptr`
         ParseException err;
-        if( !fside.equals("else") && (err = ret.err()) !=null ) throw err;
+        if( !fside.equals("else") && (err = ret.err()) !=null ) throw Parser.error(err.getMessage(),site);
         ret.keep();
         r.peephole();
         return ret.unkeep();
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/Declarations.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/Declarations.java
index 91955197..13fa59b8 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/parser/Declarations.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/Declarations.java
@@ -47,15 +47,17 @@ final class Declarations {
         boolean inferType = t==Type.TOP || t==Type.BOTTOM;
         boolean xfinal = bindingFinal(t);
         Lexer loc = P.loc();
-        String name = P.requireId();
+        String name = P.requireId(P._scope.klast() instanceof Kind.Func fun && FunNode.isInit(fun._name));
         // Optional initializing expression follows
         boolean fld_final = false; // Field is final, but not deeply final
         boolean uninit = false;    // Required non-null constructor field
         Node expr;
         if( P.match("=") ) {
+            P._lexer.skipWhiteSpace();
+            Lexer initializer=P.loc();
             if( isExternDecl() ) {
                 if( !(t instanceof TypeFunPtr) ) {
-                    Node ptr = externData(name,t);
+                    Node ptr = externData(name,t,loc);
                     // The lexical binding is a fixed address; its contents are mutable.
                     if( !P._scope.define(name,t,true,ptr,loc) )
                         throw Parser.error("Redefining name '"+name+"'",loc);
@@ -72,8 +74,12 @@ final class Declarations {
             // var/val, then type comes from expression
             if( inferType ) {
                 if( expr._type==Type.NIL )
-                    throw P.error("a not-null/non-zero expression");
+                    throw Parser.error("Cannot infer a type from null; declare a nullable type explicitly",initializer);
                 t = expr._type;
+                // A typed expression may still await a forward callee's flow
+                // type (e.g. interpolation while sys.text is parsed). Its
+                // checked conversion already supplies a binding/storage type.
+                if( t==Type.BOTTOM && expr instanceof ConvertNode convert ) t=convert.dst();
                 if( !xfinal ) t = Conversions.mutableInferredType(t);
                 // Instance fields may change until the constructor finishes.
                 // Keep the declared family/access, not the default's constant
@@ -133,8 +139,7 @@ final class Declarations {
     // Just after parsing "type foo = " can parse `"C"`
     private boolean isExternDecl( ) {
         int old = P.pos();
-        String s = P._lexer.parseString();
-        if( "C".equals(s) ) return true;
+        if( P.match("\"C\"") ) return true;
         P.pos(old);
         return false;
     }
@@ -151,14 +156,14 @@ final class Declarations {
 
     // A lexical C binding has a singleton namespace with one external field.
     // The namespace occupies no storage; its field offset supplies the address.
-    private Node externData(String name, Type t) {
+    private Node externData(String name, Type t, Lexer site) {
         if( !(t instanceof TypeInteger) && !(t instanceof TypeFloat) )
-            throw P.error("C data binding requires an integer or float type");
+            throw Parser.error("C data binding requires an integer or float type",site);
         String cname = ("C:"+name).intern();
         TypeStruct ts = TypeStruct.make(cname,false,Field.make(name,t,P._code.externAlias(name),false,true));
         Type old = Parser.TYPES.putIfAbsent(cname,ts);
         if( old!=null && old!=ts )
-            throw P.error("Conflicting types for C data '"+name+"'");
+            throw Parser.error("Conflicting types for C data '"+name+"'",site);
         return P.con(TypeMemPtr.make((byte)2,ts,true));
     }
 }
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/Expressions.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/Expressions.java
index 93c07d8a..247d974e 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/parser/Expressions.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/Expressions.java
@@ -15,6 +15,8 @@ final class Expressions {
     /** Parse: [name '='] expr
      */
     Node parseAssignment() {
+        P._lexer.skipWhiteSpace();
+        Lexer site=P.loc();
         int old = P.pos();
         String name = P._lexer.matchId();
         // Just a plain expression, no assignment.
@@ -24,13 +26,16 @@ final class Expressions {
 
         // Find variable to update
         Var def = P._scope.lookup(name);
-        if( def==null )
+        if( def==null ) {
+            P.pos(old);
+            P._lexer.skipWhiteSpace();
             throw P.error("Undefined name '" + name + "'");
+        }
 
         if( def._extern!=0 )    // Parse the C binding as a memory lvalue
             {  P.pos(old);  return parseExpression();  }
 
-        P.references.checkAssignment(def);
+        P.references.checkAssignment(def,site);
         return P.references.assign(def,parseAssignment());
     }
 
@@ -117,6 +122,8 @@ final class Expressions {
         Node cmp = makeCompBool(dir,lhs.unkeep(),rhs).keep(); // Convert to a bool
 
         // Stacked compares?
+        P._lexer.skipWhiteSpace();
+        Lexer operator=P.loc();
         int dir0 = parseCompDir();
         if( dir0 == 0 ) {
             rhs.unkill();
@@ -137,7 +144,7 @@ final class Expressions {
         // compares (LHS:b < RHS:c) then (LHS:c < RHS:d), etc.
         while( dir0 != 0 ) {
             if( Math.abs(dir) != Math.abs(dir0) )
-                throw P.error("Mixing relational directions in a chained relational test");
+                throw Parser.error("Mixing relational directions in a chained relational test",operator);
             // True side parses next arm of test
             P.ctrl(ifT.unkeep());
             lhs = rhs;          // Reuse the previous RHS exactly once
@@ -150,6 +157,8 @@ final class Expressions {
             P.ctrl(ifF);
             fail.mergeScopes(P._scope.dup(), P.loc()).peephole();
             // Check next stacked compare
+            P._lexer.skipWhiteSpace();
+            operator=P.loc();
             dir0 = parseCompDir();
         }
         rhs.unkill();
@@ -185,9 +194,11 @@ final class Expressions {
     private Node parseShift() {
         Node lhs = parseAddition();
         while( true ) {
-            if( P.match("<<") ) lhs = new ShlNode(P.loc(),lhs,null);
-            else if( P.match(">>>")) lhs = new ShrNode(P.loc(),lhs,null);
-            else if( P.match(">>") ) lhs = new SarNode(P.loc(),lhs,null);
+            P._lexer.skipWhiteSpace();
+            Lexer site=P.loc();
+            if( P.match("<<") ) lhs = new ShlNode(site,lhs,null);
+            else if( P.match(">>>")) lhs = new ShrNode(site,lhs,null);
+            else if( P.match(">>") ) lhs = new SarNode(site,lhs,null);
             else break;
             lhs.setDef(2,parseAddition());
             ParseException err;
@@ -251,12 +262,14 @@ final class Expressions {
         int old = P.pos();
         if( P.match("--") || P.match("++") ) {
             int delta = P._lexer.peek(-1)=='+' ? 1 : -1; // Inc vs Dec
+            P._lexer.skipWhiteSpace();
             int start = P.pos();
+            Lexer site=P.loc();
             String name = P._lexer.matchId();
             Var var = name==null ? null : P._scope.lookup(name);
             if( var!=null && !(var.type() instanceof TypeMemPtr) ) {
                 if( var._extern==0 && var._final && !P._scope.canInit(var) )
-                    throw P.error("Cannot reassign final '"+var._name+"'");
+                    throw Parser.error("Cannot reassign final '"+var._name+"'",site);
                 // Resolve fields just as a read or postfix update does. Updating
                 // their declaration's local slot would silently lose the Store.
                 P.pos(start);
@@ -286,7 +299,7 @@ final class Expressions {
     // pre is +/-1 for a prefix update of a known name, zero otherwise.
     private Node parsePrimary(int pre) {
         if( P._lexer.isNumber(P._lexer.peek()) ) return parseLiteral();
-        if( P._lexer.peek('"') ) return parsePostfix(P.allocations.newString(P._lexer.parseString()));
+        if( P._lexer.peek('"') ) return parsePostfix(P.strings.parse());
         if( P.matchx("true" ) ) return P.con(1);
         if( P.matchx("false") ) return P._code.ZERO;
         if( P.matchx("null" ) ) return P.con(Type.NIL);
@@ -298,8 +311,10 @@ final class Expressions {
         int pos = P.pos();
         // Expect an identifier now
         String id = P._lexer.matchId();
-        if( id == null || Parser.KEYWORDS.contains(id) )
+        if( id == null || Parser.KEYWORDS.contains(id) ) {
+            P.pos(pos);
             throw P.errorSyntax("an identifier or expression");
+        }
         int pos2 = P.pos();
         return P.references.parseName(id,pre,pos,pos2);
     }
@@ -366,7 +381,11 @@ final class Expressions {
         P._lexer.skipWhiteSpace();
         Lexer site = P.loc();
         String name;
-        if( P.match(".") )      name = P.requireId();
+        if( P.match(".") ) {
+            P._lexer.skipWhiteSpace();
+            site=P.loc();
+            name = P.requireId(true);
+        }
         else if( P.match("#") ) name = "#";
         else if( P.match("[") ) name = "[]";
         // Can get here without an explicit receiver: "f()" or
@@ -389,6 +408,6 @@ final class Expressions {
 
     // Already parsed "'"
     Node parseChar() {
-        return P.require(P.con(TypeInteger.constant(P._lexer.parseChar())),"'");
+        return P.con(TypeInteger.constant(P._lexer.parseChar()));
     }
 }
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/Functions.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/Functions.java
index 14dee33b..5175acc6 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/parser/Functions.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/Functions.java
@@ -73,14 +73,19 @@ final class Functions {
         while( true ) {
             Type t = P.types.parseType();    // Arg type
             if( t==null ) break;
+            P._lexer.skipWhiteSpace();
+            Lexer qualifier=P.loc();
             if( P.match("^") ) {
                 if( !(t instanceof TypeMemPtr ptr) || ptr._obj.isAry() )
-                    throw P.error("'^' requires a struct parameter");
+                    throw Parser.error("'^' requires a struct parameter",qualifier);
                 t = ptr.withPartial(true);
                 P.construction._borrowed = true;
             }
             finals.set(ids.size(),P.declarations.bindingFinal(t));
+            P._lexer.skipWhiteSpace();
+            Lexer nameLoc=P.loc();
             String id = P.requireId();
+            if( ids.find(id)!=-1 ) throw Parser.error("Duplicate parameter '"+id+"'",nameLoc);
             ts .push(t );       // Push type/arg pairs
             ids.push(id);
             P.match(",");
@@ -98,7 +103,7 @@ final class Functions {
         Lexer site = P.loc();
         site._position--; // Opening '('; arguments can contain nested calls.
         if( fcn._type == Type.NIL )
-            throw P.error("Calling a null function pointer");
+            throw Parser.error("Calling a null function pointer",site);
         fcn.keep();            // Keep while parsing args
 
         Ary<Node> args = new Ary<>( Node.class );
@@ -207,6 +212,9 @@ final class Functions {
 
         int oldUID = P._code.UID(); // Used to approximate function size
         FunNode fun = enterFunction(funName,sig,loc,finals,ids);
+        // Guards belong to this function's control flow. Do not inherit an
+        // enclosing function's predicates or leak this body's guards on exit.
+        P._scope.addGuards(fun,null,false);
         Construction.Frame outerConstruction = P.construction.enter(fun,isCtor && !fun.isClz());
         Node rpc = fun.parm(0);
         if( fun.isClz() ) P.structs.beginClassInit(fun,loc);
@@ -260,6 +268,7 @@ final class Functions {
         P._ref.addFun(P._code,fun);
 
         // Unstack parser state
+        P._scope.removeGuards(fun);
         if( _returnScope != null ) _returnScope.kill();
         _returnScope   =   returnScope;
         P.statements._continueScope = continueScope;
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/Lexer.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/Lexer.java
index ec88738b..5e4b7311 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/parser/Lexer.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/Lexer.java
@@ -3,10 +3,12 @@ package com.seaofnodes.simple.parser;
 import com.seaofnodes.simple.codegen.CodeGen;
 import com.seaofnodes.simple.codegen.CompUnit;
 import com.seaofnodes.simple.codegen.Serialize;
+import com.seaofnodes.simple.codegen.SourceError;
 import com.seaofnodes.simple.parser.Parser.ParseException;
 import com.seaofnodes.simple.type.*;
 import com.seaofnodes.simple.util.BAOS;
 import java.util.HashMap;
+import java.io.ByteArrayOutputStream;
 
 // Lexer provides low level access to the raw file bytes, peeks and matches
 // short strings, parses numbers, skips comments and whitespace, tracks
@@ -35,6 +37,11 @@ public class Lexer {
     public String position() { return _line_number+":"+(_position-_line_start+1); }
     public int pos() { return _position; }
 
+    public String diagnostic(String message) {
+        return _cu==null ? SourceError.format("<input>",_input,_position,message)
+            : SourceError.format(_cu,_position,message);
+    }
+
     /**
      * Record the source text for lexing
      */
@@ -143,19 +150,21 @@ public class Lexer {
         while( true ) {
             if( isWhiteSpace() ) inc();
             // Skip // to end of line
-            else if( _position+2 < _input.length &&
+            else if( _position+1 < _input.length &&
                      _input[_position  ] == '/' &&
                      _input[_position+1] == '/') {
                 inc(); inc();
                 while( !isEOF() && _input[_position] != '\n' )
                     inc();
-            } else if( _position+2 < _input.length &&
+            } else if( _position+1 < _input.length &&
                      _input[_position  ] == '/' &&
                      _input[_position+1] == '*') {
-                // Skip /*comment*/
-                while( !isEOF() && !(_input[_position-1] == '*' && _input[_position] == '/'))
+                Lexer start=new Lexer(this);
+                inc(); inc();
+                while( !isEOF() && !(peek()=='*' && _position+1<_input.length && peek(1)=='/') )
                     inc();
-                inc();
+                if( isEOF() ) throw Parser.error("Unclosed block comment",start);
+                inc(); inc();
             } else break;
         }
     }
@@ -229,20 +238,27 @@ public class Lexer {
 
     // Return a constant Type, either TypeInteger or TypeFloat
     Type parseNumber() {
+        Lexer start=new Lexer(this);
         int old = _position;
         int len = isLongOrDouble();
         boolean f32 = peek()=='f';
         if( f32 ) nextChar();
         int n = Math.abs(len);
-        if( f32 )
-            return TypeFloat.constant(Float.parseFloat(new String(_input,old,n)));
-        if( len > 0 ) {
-            if( len > 1 && _input[old]=='0' )
-                throw Parser.error("Syntax error: integer values cannot start with '0'",this);
-            long i = Long.parseLong(new String(_input,old,len));
-            return TypeInteger.constant(i);
+        String literal=new String(_input,old,n);
+        try {
+            if( f32 )
+                return TypeFloat.constant(Float.parseFloat(literal));
+            if( len > 0 ) {
+                if( len > 1 && _input[old]=='0' )
+                    throw Parser.error("Syntax error: integer values cannot start with '0'",start);
+                long i = Long.parseLong(literal);
+                return TypeInteger.constant(i);
+            }
+            return TypeFloat.constant(Double.parseDouble(literal));
+        } catch( NumberFormatException ex ) {
+            throw Parser.error(len>0 && !f32 ? "Integer literal is outside the signed 64-bit range"
+                : "Invalid floating-point literal '"+literal+(f32 ? "f" : "")+"'",start);
         }
-        return TypeFloat.constant(Double.parseDouble(new String(_input,old,n)));
     }
     private String parseNumberString() {
         int old = _position;
@@ -319,25 +335,77 @@ public class Lexer {
         return 0;
     }
 
-    String parseString() {
-        if( !peek('"') ) return null;
-        inc();
-        StringBuilder sb = new StringBuilder();
+    record StringPart(byte[] text, boolean end) {}
+
+    // Opening quote has been consumed. Leave a format's '%' unread so both
+    // the expression parser and deferred-body scanner use the same grammar.
+    StringPart stringPart(Lexer start) {
+        ByteArrayOutputStream sb = new ByteArrayOutputStream();
         while( !isEOF() ) {
             char c = nextChar();
-            if( c=='"' ) return sb.toString();
+            if( c=='"' ) return new StringPart(sb.toByteArray(),true);
+            if( c=='%' ) {
+                if( peek()=='%' ) { inc(); sb.write('%'); continue; }
+                _position--;
+                return new StringPart(sb.toByteArray(),false);
+            }
             if( c!='\\' ) {
-                sb.append(c);
+                sb.write(c);
                 continue;
             }
             if( isEOF() )
-                throw error("Unclosed string");
-            sb.append(escapedChar("string"));
+                throw Parser.error("Unclosed string",start);
+            sb.write(escapedChar("string"));
         }
-        throw error("Unclosed string");
+        throw Parser.error("Unclosed string",start);
+    }
+
+    record Format(int kind, int flags, int width, int precision, Lexer site) {}
+
+    Format stringFormat() {
+        Lexer site = new Lexer(this);
+        assert peek()=='%';
+        inc();
+        if( peek()=='(' ) { inc(); return new Format(0,0,0,-1,site); }
+        int flags=0, bit;
+        while( (bit="-+ #0".indexOf(peek()))>=0 ) {
+            int mask=1<<bit;
+            if( (flags&mask)!=0 ) throw Parser.error("Repeated format flag",site);
+            flags |= mask;
+            inc();
+        }
+        int width = formatNumber(site);
+        int precision = -1;
+        if( peek()=='.' ) {
+            inc();
+            precision = formatNumber(site);
+        }
+        char kind=nextChar();
+        if( "diuoxXfFeEgGaAcsb".indexOf(kind)<0 )
+            throw Parser.error("Expected a string format: %(expression), %d(expression), or %%",site);
+        boolean number="diuoxXfFeEgGaA".indexOf(kind)>=0;
+        if( !number && (flags&~1)!=0 || "uoxX".indexOf(kind)>=0 && (flags&6)!=0 ||
+            "diu".indexOf(kind)>=0 && (flags&8)!=0 )
+            throw Parser.error("Invalid flags for %"+kind,site);
+        if( precision>=0 && (kind=='c' || kind=='b') )
+            throw Parser.error("Precision is not supported for %"+kind,site);
+        if( peek()!='(' ) throw Parser.error("Expected '(' after string format %"+kind,site);
+        inc();
+        return new Format(kind,flags,width,precision,site);
+    }
+
+    private int formatNumber(Lexer site) {
+        long n=0;
+        while( peek()>='0' && peek()<='9' ) {
+            n=n*10+nextChar()-'0';
+            if( n>Integer.MAX_VALUE ) throw Parser.error("String format width or precision is too large",site);
+        }
+        return (int)n;
     }
 
     private char escapedChar(String kind) {
+        Lexer start=new Lexer(this);
+        start._position--; // The backslash introducing the escape.
         char esc = nextChar();
         return switch( esc ) {
         case '0'  -> '\u0000';
@@ -347,17 +415,24 @@ public class Lexer {
         case '\\' -> '\\';
         case '"'  -> '"';
         case '\'' -> '\'';
-        default -> throw error("Unknown "+kind+" escape \\\\"+esc);
+        case '%'  -> '%';
+        default -> throw Parser.error("Unknown "+kind+" escape \\"+esc,start);
         };
     }
 
     char parseChar() {
-        if( isEOF() ) throw error("Unclosed character");
+        Lexer start=new Lexer(this);
+        start._position--; // Opening quote was consumed by the caller.
+        if( isEOF() || peek()=='\n' || peek()=='\r' ) throw Parser.error("Unclosed character literal",start);
+        if( peek()=='\'' ) throw Parser.error("Empty character literal",start);
         char c = nextChar();
         if( c=='\\' ) {
-            if( isEOF() ) throw error("Unclosed character");
+            if( isEOF() ) throw Parser.error("Unclosed character literal",start);
             c = escapedChar("character");
         }
+        if( isEOF() || peek()=='\n' || peek()=='\r' ) throw Parser.error("Unclosed character literal",start);
+        if( peek()!='\'' ) throw Parser.error("Character literal must contain exactly one byte",start);
+        inc();
         return c;
     }
 
@@ -372,16 +447,18 @@ public class Lexer {
             if( isEOF() ) throw error("Unclosed "+what);
             char ch = peek();
             if( ch==close && depth==0 ) return;
+            Lexer site=ch=='"' ? new Lexer(this) : null;
             nextChar();
             if( ch==open ) depth++;
             else if( ch==close ) depth--;
-            else if( ch=='"' || ch=='\'' ) {
-                char quote = ch;
-                while( !isEOF() ) {
-                    ch = nextChar();
-                    if( ch=='\\' ) nextChar();
-                    else if( ch==quote ) break;
+            else if( ch=='"' ) {
+                while( !stringPart(site).end() ) {
+                    stringFormat();
+                    skipTo('(',')',"string interpolation");
+                    nextChar();
                 }
+            } else if( ch=='\'' ) {
+                parseChar();
             }
         }
     }
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/Parser.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/Parser.java
index 4d140e55..0cf3c0e7 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/parser/Parser.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/Parser.java
@@ -24,6 +24,7 @@ public class Parser {
     final References references = new References(this);
     final Conversions conversions = new Conversions(this);
     final Construction construction = new Construction(this);
+    final Strings strings = new Strings(this);
 
     public void checkConstructionSerializable() { construction.checkSerializable(); }
 
@@ -106,7 +107,7 @@ public class Parser {
             put("i32" ,TypeInteger.I32);
             put("i64" ,TypeInteger.BOT);
             put("i8"  ,TypeInteger.I8 );
-            put("int" ,TypeInteger.BOT);
+            put("int" ,TypeInteger.I32);
             put("u1"  ,TypeInteger.U1 );
             put("u16" ,TypeInteger.U16);
             put("u32" ,TypeInteger.U32);
@@ -117,7 +118,8 @@ public class Parser {
 
     public static class ParseException extends RuntimeException {
         public final Lexer _loc;
-        ParseException( String msg, Lexer loc ) { super(msg);  _loc = loc; }
+        ParseException( String msg, Lexer loc ) { super(msg); _loc = loc==null ? null : new Lexer(loc); }
+        public String diagnostic() { return _loc==null ? getMessage() : _loc.diagnostic(getMessage()); }
     }
 
     public Parser(CodeGen code ) {
@@ -186,9 +188,18 @@ public class Parser {
 
     // Require and return an identifier
     String requireId() {
+        return requireId(false);
+    }
+
+    // Primitive names are useful member names (sys.text.int), but remain
+    // reserved for local variables, parameters and type declarations.
+    String requireId(boolean member) {
+        _lexer.skipWhiteSpace();
+        Lexer site=loc();
         String id = _lexer.matchId();
-        if (id != null && !KEYWORDS.contains(id) ) return id.intern();
-        throw error("Expected an identifier, found '"+id+"'");
+        if (id != null && (!KEYWORDS.contains(id) || member &&
+            (INIT_TYPES.get(id) instanceof TypeInteger || INIT_TYPES.get(id) instanceof TypeFloat)) ) return id.intern();
+        throw error("Expected an identifier, found '"+new Lexer(site).getAnyNextToken()+"'",site);
     }
 
     String matchId() {
@@ -266,7 +277,9 @@ public class Parser {
 
     ParseException errorSyntax(String syntax) { return _errorSyntax("expected `"+syntax+"`");  }
     private ParseException _errorSyntax(String msg) {
-        return error("Syntax error, "+msg+" but found `" + _lexer.getAnyNextToken()+"`");
+        _lexer.skipWhiteSpace();
+        // Reading the token for the message must not advance the error location.
+        return error("Syntax error, "+msg+" but found `" + loc().getAnyNextToken()+"`");
     }
     ParseException error(String msg) { return error(msg,_lexer); }
     public static ParseException error(String msg, Lexer loc) { return new ParseException(msg,loc); }
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/References.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/References.java
index 483bd7a8..6335bad2 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/parser/References.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/References.java
@@ -15,13 +15,36 @@ final class References {
 
     References(Parser P) { this.P = P; }
 
+    // Compiler-generated library references use ordinary module lookup and
+    // forward resolution, without a synthetic token stream.
+    Node classReference(String name, Lexer site) {
+        CompUnit cu=ParseAll.findCompUnit(P._code,P._ref,name);
+        if( cu==null ) throw Parser.error("Cannot find standard library '"+name+"'",site);
+        String clzName=TypeStruct.addClzPrefix(cu._cname);
+        TypeStruct clz=(TypeStruct)Parser.TYPES.computeIfAbsent(clzName,n -> TypeStruct.make(n,true));
+        FRefNode ref=new FRefNode(name,site,TypeMemPtr.make((byte)2,clz,true));
+        _frefs.push(ref);
+        return ref.peephole();
+    }
+
+    // Read a member without consuming a postfix from source text.
+    Node member(Node receiver, String name, Lexer site) {
+        Field fld=receiver._type instanceof TypeMemPtr ptr ? ptr._obj.field(name) : null;
+        return P.peep(new LoadNode(site,name,fld==null ? 1 : fld._alias,
+                                  P.ctrl(),P.mem(),receiver,P.fldoff(receiver,name)));
+    }
+
     // Resolve a primary name, retaining its use site before speculative type lookup.
     Node parseName(String id, int pre, int pos, int pos2) {
+        Lexer site=P.loc();
+        site._position=pos;
+        site.skipWhiteSpace();
         // Attempt a local var lookup first
         Var var = P._scope.lookup(id);
         if( var==null ) {
             // Not a local var, try again as a type name
             P.pos(pos);
+            Lexer nameLoc = P.loc();
             Type t = P.types.parseType();
             if( t!=null ) {
                 // Static <clinit> typename lookup
@@ -52,7 +75,7 @@ final class References {
                 t = TypeMemPtr.make((byte)2,clz,true);
             }
             // Define the FRef
-            var = P._scope.defineFRef(id,t,true,P.loc());
+            var = P._scope.defineFRef(id,t,true,nameLoc);
             P.references._frefs.push((FRefNode)P._scope.in(var));
         }
 
@@ -73,7 +96,7 @@ final class References {
         if( kx < fx && !P.structs.inExplicitConstructor() && // Out of scope
             !(var._final && rvalue._type.isConstant()) ) { // Not a final constant
             if( kx > 0  ) // Global scope is OK, only ever one of these (not one per function invoke)
-                throw P.error("Variable '"+var._name+"' is out of function scope and must be a final constant");
+                throw Parser.error("Variable '"+var._name+"' is out of function scope and must be a final constant",site);
 
             // var.idx==2 is self argument, 3 is args, 4 or more are now static globals
             if( var._idx >= 4 ) {
@@ -98,7 +121,7 @@ final class References {
         }
         // Assign-update direct into Scope
         if( var._final && !P._scope.canInit(var) )
-            throw P.error("Cannot reassign final '"+var._name+"'");
+            throw Parser.error("Cannot reassign final '"+var._name+"'",site);
         checkSharedFunction(var);
         Node op = P.expressions.opAssign(ch,rvalue, var.type() );
         P._scope.update(var,op);
@@ -106,14 +129,14 @@ final class References {
         return pre==0 && Lexer.postfix(ch) ? rvalue : op;
     }
 
-    void checkAssignment(Var def) {
+    void checkAssignment(Var def, Lexer site) {
         String name = def._name;
         // A final field may receive its first value in its constructor.
         if( P._scope.in(def._idx)._type!=Type.TOP && def._final &&
             // Inside an allocation, final assign is OK, outside nope.
             // The parseNew() call added the allocation scope
             !P._scope.canInit(def) )
-            throw P.error("Cannot reassign final '"+name+"'");
+            throw Parser.error("Cannot reassign final '"+name+"'",site);
         checkSharedFunction(def);
 
     }
@@ -201,7 +224,7 @@ final class References {
         if( fld==null && ts!=null )
             fld = P.types.fieldOrOpen(ts,name,false);
         if( fld==null && ts!=null && !P.types.latestStruct(ts)._open )
-            throw P.error("Accessing unknown field '"+name+"' from '*"+ts._name+"'");
+            throw Parser.error("Accessing unknown field '"+name+"' from '*"+ts._name+"'",site);
 
         // We have to record "active touches" of a new class, to track when we
         // need to force class initialization.  Basically, we insert an CLInit,
@@ -233,7 +256,7 @@ final class References {
             // Store to field
             mem.keep();
             if( !P.construction.own(expr) && expr._type instanceof TypeMemPtr view && view._ro && P.ctrl()._type!=Type.XCONTROL )
-                throw P.error("Cannot modify final field '"+name+"'");
+                throw Parser.error("Cannot modify final field '"+name+"'",site);
             Node st = new StoreNode(P.loc(), name, alias, decl, P.ctrl(), mem, expr.unkeep(), off.unkeep(), lift, P.construction.own(expr)).peephole().keep();
             P.construction.store(expr,alias,st,mem);
             st.unkeep();
@@ -250,17 +273,17 @@ final class References {
             decl = conary.elem();
 
         // Load field
-        Node load = P.peep(new LoadNode(P.loc(),name,alias,P.ctrl(),mem,expr,off));
+        Node load = P.peep(new LoadNode(site,name,alias,P.ctrl(),mem,expr,off));
 
         // Check for assign-update, "ptr.fld += expr" or "ary[idx]++"
         char ch = pre==0 ? P._lexer.matchOperAssign() : (char)pre;
         if( ch!=0 ) {
             if( fld!=null && decl==Type.BOTTOM )
-                throw P.error( "'" + ts._name + "' is not fully initialized, field '" + fld._fname + "' needs to be set in a constructor" );
+                throw Parser.error( "'" + ts._name + "' is not fully initialized, field '" + fld._fname + "' needs to be set in a constructor",site );
             Node op = P.expressions.opAssign(ch,load, decl ).keep();
             mem.keep();
             if( !P.construction.own(expr) && expr._type instanceof TypeMemPtr view && view._ro && P.ctrl()._type!=Type.XCONTROL )
-                throw P.error("Cannot modify final field '"+name+"'");
+                throw Parser.error("Cannot modify final field '"+name+"'",site);
             Node st = new StoreNode(P.loc(), name, alias, decl, P.ctrl(), mem, expr.unkeep(), off.unkeep(), op, P.construction.own(expr)).peephole().keep();
             P.construction.store(expr,alias,st,mem);
             st.unkeep();
@@ -302,7 +325,8 @@ final class References {
         Ary<FRefNode> frefs = new Ary<>(FRefNode.class);
         for( FRefNode fref : _frefs ) {
             if( fref.nIns() != 1 && fref._con == FRefNode.FREF_TYPE ) continue;
-            CompUnit cu = ParseAll.findCompUnitOrThrow(P._code,P._ref,fref._name);
+            CompUnit cu = ParseAll.findCompUnit(P._code,P._ref,fref._name);
+            if( cu==null ) throw fref.err();
             // Name lookup may already know this class's fields. Do not replace
             // that information with an empty placeholder before Iter runs.
             if( fref._con==FRefNode.FREF_TYPE )
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/Statements.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/Statements.java
index 4ff4993b..707202ab 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/parser/Statements.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/Statements.java
@@ -24,12 +24,14 @@ final class Statements {
      * @return a {@link Node} or {@code null}
      */
     Node parseStatement() {
+        P._lexer.skipWhiteSpace();
+        Lexer site=P.loc();
         if(      P.matchx("return")  ) return parseReturn();
         else if (P.matchx("if")      ) return parseIf();
         else if (P.matchx("while")   ) return parseWhile();
         else if (P.matchx("for")     ) return parseFor();
-        else if (P.matchx("break")   ) return parseBreak();
-        else if (P.matchx("continue")) return parseContinue();
+        else if (P.matchx("break")   ) return parseBreak(site);
+        else if (P.matchx("continue")) return parseContinue(site);
         else if (P.matchx("struct")  ) return P.structs.parseStruct();
         else if (P.structs.inStructDeclaration() && P.matchx("new")) return P.structs.parseConstructorDeclaration();
         else if (P.matchx(";")       ) return P._code.ZERO; // Empty statement
@@ -204,7 +206,7 @@ final class Statements {
         if( doFor ) {
             int old = P.pos(nextPos);
             if( !P.peek(')') )
-              P.expressions.parseAssignment();
+              P.expressions.parseAssignment().isKill();
             if( P.pos() != nextEnd )
                 throw P.errorSyntax( "Unexpected code after expression" );
             P.pos(old);
@@ -237,8 +239,8 @@ final class Statements {
         P._scope = exit;
         return P._code.ZERO;
     }
-    private Node parseBreak   () {
-        checkLoopActive();
+    private Node parseBreak(Lexer site) {
+        checkLoopActive(site);
         // At the time of the break, and loop-exit conditions are only valid if
         // they are ALSO valid at the break.  It is the intersection of
         // conditions here, not the union.
@@ -248,15 +250,20 @@ final class Statements {
         return P._code.ZERO;
     }
 
-    private Node parseContinue() { checkLoopActive(); _continueScope = P.require(jumpTo( _continueScope ),";"); return P._code.ZERO; }
+    private Node parseContinue(Lexer site) { checkLoopActive(site); _continueScope = P.require(jumpTo( _continueScope ),";"); return P._code.ZERO; }
 
     private ScopeNode jumpTo(ScopeNode toScope) {
         ScopeNode cur = P._scope.dup();
         P.ctrl(P._code.XCTRL); // Kill current scope
         // Prune nested lexical scopes that have depth > than the loop head
         // We use _breakScope as a proxy for the loop head scope to obtain the depth
+        // The clone shares lexical boundaries and Var records with the active
+        // parser scope. Promoting on the clone would move those boundaries
+        // without moving the active scope's bindings. Drop locals first, then
+        // copy forward references into the jump scope with their own indices.
         while( cur.depth() > _breakScope.depth() )
-            cur.pop();
+            cur._pop();
+        cur.balanceLoopFRefs(P._scope);
         // If this is a continue then first time the target is null
         // So we just use the pruned current scope as the base for the
         // "continue"
@@ -264,9 +271,13 @@ final class Statements {
             return cur;
         // toScope is either the break scope, or a scope that was created here
         assert toScope.depth() <= _breakScope.depth();
+        // A later path can discover forward references after an earlier
+        // break/continue saved its scope. Keep those bindings across the merge.
+        toScope.balanceLoopFRefs(cur);
+        cur.balanceLoopFRefs(toScope);
         toScope.ctrl(toScope.mergeScopes(cur,P.loc()).peephole());
         return toScope;
     }
 
-    private void checkLoopActive() { if (_breakScope == null) throw P.error("No active loop for a break or continue"); }
+    private void checkLoopActive(Lexer site) { if (_breakScope == null) throw Parser.error("No active loop for a break or continue",site); }
 }
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/Strings.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/Strings.java
new file mode 100644
index 00000000..5bf76585
--- /dev/null
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/Strings.java
@@ -0,0 +1,59 @@
+package com.seaofnodes.simple.parser;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.*;
+import com.seaofnodes.simple.util.Ary;
+
+/** Interpolation expands to ordinary sys.text calls. The library itself uses
+ * no interpolation, so it can be compiled from source without staging. */
+final class Strings {
+    private final Parser P;
+    Strings(Parser p) { P=p; }
+
+    Node parse() {
+        Lexer start=P.loc();
+        P.require("\"");
+        Lexer.StringPart part=P._lexer.stringPart(start);
+        if( part.end() ) return P.allocations.newString(part.text());
+        Node text=P.references.classReference("sys.text",P.loc()).keep();
+        P.classInit(P.loc(),text);
+        Node builder=call(text,"begin",P.loc()).keep();
+        while( true ) {
+            if( part.text().length!=0 )
+                call(text,"string",P.loc(),builder,P.allocations.newString(part.text()),P.con('s'),P.con(0),P.con(-1)).isKill();
+            if( part.end() ) break;
+            Lexer.Format fmt=P._lexer.stringFormat();
+            Node value=P.expressions.parseAssignment().keep();
+            P.require(")");
+            Node fptr;
+            if( fmt.kind()==0 ) {
+                Node ints=P.references.member(text,"integer",fmt.site()).keep();
+                Node floats=P.references.member(text,"floating",fmt.site()).keep();
+                Node strings=P.references.member(text,"string",fmt.site()).keep();
+                fptr=new FormatNode(value,ints.unkeep(),floats.unkeep(),strings.unkeep(),fmt.site()).peephole();
+            } else {
+                String family="diuoxXcb".indexOf(fmt.kind())>=0 ? "integer" : fmt.kind()=='s' ? "string" : "floating";
+                fptr=P.references.member(text,family,fmt.site());
+            }
+            call(text,fptr,fmt.site(),builder,value.unkeep(),P.con(fmt.kind() | fmt.flags()<<8),
+                 P.con(fmt.width()),P.con(fmt.precision())).isKill();
+            part=P._lexer.stringPart(start);
+        }
+        // String syntax promises this result type even when sys.text is still
+        // awaiting its source parse. Check/convert through the normal IR.
+        Node result=call(text.unkeep(),"end",P.loc(),builder.unkeep());
+        return P.conversions.convertExpr(result,TypeMemPtr.make(P.types.typeAry(TypeInteger.U8,true)).makeRO());
+    }
+
+    private Node call(Node text, String name, Lexer site, Node... values) {
+        return call(text,P.references.member(text,name,site),site,values);
+    }
+
+    private Node call(Node text, Node fptr, Lexer site, Node... values) {
+        Ary<Node> args=new Ary<>(Node.class);
+        args.push(P.ctrl()); args.push(P.mem()); args.push(text);
+        for( Node value:values ) args.push(value);
+        args.push(fptr);
+        return P.functions.functionCall(args,site);
+    }
+}
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/Structs.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/Structs.java
index a5262440..3a3d894c 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/parser/Structs.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/Structs.java
@@ -78,12 +78,14 @@ final class Structs {
     Node parseConstructorDeclaration() {
         TypeStruct self = P._scope.constructorSelf();
         assert self != null;
+        P._lexer.skipWhiteSpace();
+        Lexer site=P.loc();
         String name = P.requireId();
         String expect = initFieldName(self._name);
         if( name != expect )
-            throw P.error("Constructor name '" + name + "' must match type name '" + expect + "'");
+            throw Parser.error("Constructor name '" + name + "' must match type name '" + expect + "'",site);
         P.require("=");
-        if( _pendingCtor!=null ) throw P.error("Redefining constructor '"+name+"'");
+        if( _pendingCtor!=null ) throw Parser.error("Redefining constructor '"+name+"'",site);
         _pendingCtor = new Constructor(name,P.loc());
         // Parse the body after all field declarations are known, so self.x
         // and x resolve the same field even when x is declared below this body.
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/parser/Types.java b/chapter30/src/main/java/com/seaofnodes/simple/parser/Types.java
index ffd3a0f4..827518fd 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/parser/Types.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/parser/Types.java
@@ -54,12 +54,14 @@ final class Types {
         // Nest arrays and '?' as needed
         Type t2 = t1;
         while( true ) {
+            P._lexer.skipWhiteSpace();
+            Lexer site=P.loc();
             if( P.match("?") ) {
                 if( t2 instanceof TypeMemPtr tmp ) {
-                    if( tmp.nullable() ) throw P.error("Type "+t2+" already allows null");
+                    if( tmp.nullable() ) throw Parser.error("Type "+t2+" already allows null",site);
                     t2 = tmp.makeNullable();
                 } else
-                    throw P.error("Type "+t0+" cannot be null");
+                    throw Parser.error("Type "+t0+" cannot be null",site);
             } else if( P.match("[~]") ) {
                 t2 = TypeMemPtr.make(typeAry(t2,true)).makeRO();
             } else if( P.match("[]") ) {
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/type/TypeConAry.java b/chapter30/src/main/java/com/seaofnodes/simple/type/TypeConAry.java
index c9093e3b..9cb23e09 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/type/TypeConAry.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/type/TypeConAry.java
@@ -16,6 +16,7 @@ public abstract class TypeConAry<A> extends TypeScalar {
 
     TypeConAry( boolean any, byte widen, A ary ) { super(TCONARY); _any = any; _widen = widen; _ary = ary; }
     public static void gather(ArrayList<Type> ts) {
+        ts.add(TypeConAryB.make(""));
         ts.add(TypeConAryB.ABC);
         ts.add(TypeConAryB.ABCD);
         ts.add(TypeConAryI.I123);
@@ -36,6 +37,15 @@ public abstract class TypeConAry<A> extends TypeScalar {
     }
 
     Type ymeet( TypeInteger ti ) {
+        // Empty arrays have no observed elements: use the storage bounds.
+        // Check both endpoints just as the loop checks a nonempty body;
+        // retaining high integer inputs here preserves lattice duality.
+        if( len()==0 ) {
+            TypeInteger bound=emptyElem();
+            if( !ti.isa(TypeInteger.make(bound._min,bound._min,ti._widen)) ||
+                !ti.isa(TypeInteger.make(bound._max,bound._max,ti._widen)) )
+                return ti.meet(bound);
+        }
         // if i can isa *each* element, then maybe can keep.
         // no good to i.isa(elem()) because fails the dual
         for( int j=0; j<len(); j++ )
@@ -64,6 +74,7 @@ public abstract class TypeConAry<A> extends TypeScalar {
             return _any ? Type.TOP : BOTTOM;
         int len = len();
         long min = Long.MAX_VALUE;
+        if( len==0 ) return emptyElem();
         long max = Long.MIN_VALUE;
         for( int i=0; i<len; i++ ) {
             min = Math.min(min,at8(i));
@@ -71,6 +82,10 @@ public abstract class TypeConAry<A> extends TypeScalar {
         }
         return TypeInteger.make(min,max,_widen);
     }
+    private TypeInteger emptyElem() {
+        return log_size()==0 ? TypeInteger.make(0,255,_widen)
+            : TypeInteger.make(Integer.MIN_VALUE,Integer.MAX_VALUE,_widen);
+    }
     public abstract long at8(int idx);
     public abstract int len();
     @Override public abstract int log_size();
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/type/TypeConAryB.java b/chapter30/src/main/java/com/seaofnodes/simple/type/TypeConAryB.java
index 5877c309..84be5fb2 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/type/TypeConAryB.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/type/TypeConAryB.java
@@ -10,7 +10,7 @@ public class TypeConAryB extends TypeConAry<byte[]> {
     public static TypeConAryB make( String s ) { return make(s.getBytes()); }
     static final TypeConAryB ABC  = make("abc");
     static final TypeConAryB ABCD = make("abcd");
-    @Override public long at8(int idx) { return _ary[idx]; }
+    @Override public long at8(int idx) { return _ary[idx]&255; }
     @Override public int len() { return _ary.length; }
     @Override public int log_size() { return 0; }
     @Override public String str() { return "[\""+new String(_ary)+"\"]"; }
diff --git a/chapter30/src/main/java/com/seaofnodes/simple/type/TypeInteger.java b/chapter30/src/main/java/com/seaofnodes/simple/type/TypeInteger.java
index a0c2266d..6164f721 100644
--- a/chapter30/src/main/java/com/seaofnodes/simple/type/TypeInteger.java
+++ b/chapter30/src/main/java/com/seaofnodes/simple/type/TypeInteger.java
@@ -53,7 +53,15 @@ public class TypeInteger extends TypeScalar {
     }
 
     public Type same_but_slightly_wider_than( ) {
-        return _widen < 3 ? make(_min,_max, (byte)(_widen+1)) : BOT;
+        if( _widen < 3 ) return make(_min,_max, (byte)(_widen+1));
+        // Start in the intersection of i32 and u32 for nonnegative ranges.
+        // Widening those straight to i32 invents negative values that prevent
+        // a u32 loop from remaining unsigned. Either 32-bit range can then
+        // grow to its own bound; unbounded arithmetic ultimately reaches BOT.
+        if( _min >= 0 && _max <= I32._max ) return make(0,I32._max,(byte)3);
+        if( _min >= I32._min && _max <= I32._max ) return I32;
+        if( _min >= 0 && _max <= U32._max ) return U32;
+        return BOT;
     }
     // Force max widen
     @Override public Type widen() {
diff --git a/chapter30/src/main/smp/sys.smp b/chapter30/src/main/smp/sys.smp
index 7705a187..1201315b 100644
--- a/chapter30/src/main/smp/sys.smp
+++ b/chapter30/src/main/smp/sys.smp
@@ -7,5 +7,7 @@ val aryi64 = aryi64;            // Variable sized array of i64
 val aryu8 = aryu8;              // Variable sized array of u8
 val char = char;                // Character utilities
 val io = io;                    // IO library
+val text = text;                // Typed text conversions
 val libc = libc;                // libc FFI bindings
+val rt = rt;                    // Run Time support
 val scan = scan;                // A simple string parser
diff --git a/chapter30/src/main/smp/sys/ary.smp b/chapter30/src/main/smp/sys/ary.smp
index 8312e94c..c139cd33 100644
--- a/chapter30/src/main/smp/sys/ary.smp
+++ b/chapter30/src/main/smp/sys/ary.smp
@@ -1,11 +1,25 @@
 
 // Array utilities
 
+// Geometric growth without wrapping a u32 length. Zero means too large.
+val capacity = { u32 current, i64 needed ->
+    if( needed < 0 || needed > 4294967295 ) return 0;
+    if( needed <= current ) return current;
+    i64 size = current ? current : 1;
+    while( size < needed ) {
+        size *= 2;
+        if( size > 4294967295 ) size = 4294967295;
+    }
+    u32 result = size;
+    return result;
+};
+
 // Copy byte array contents.  Copies the shorter of the buffers and len
-val copy = { u8[] dst, int doff, u8[~] src, int soff, int len ->
+val copy = { u8[] dst, u32 doff, u8[~] src, u32 soff, u32 len ->
+    if( doff > dst# || soff > src# ) return dst;
     if( len > dst# - doff ) len = dst# - doff;
     if( len > src# - soff ) len = src# - soff;
-    for( int i=0; i<len; i++ )
+    for( u32 i=0; i<len; i++ )
         dst[i+doff] = src[i+soff];
     return dst;
 };
@@ -14,10 +28,12 @@ val copy = { u8[] dst, int doff, u8[~] src, int soff, int len ->
 // len.  Returns <0 or >0 for first non-matching byte.  Returns <0 or >0 for
 // the larger array after that, or 0 if both arrays are fully equal.
 val cmp = { u8[~] src1, u32 off1, u8[~] src2, u32 off2, u32 len ->
-    u32 len1 = len > src1# - off1 ? src1# - off1 : len;
-    u32 len2 = len > src2# - off2 ? src2# - off2 : len;
+    u32 left1 = off1 >= src1# ? 0 : src1# - off1;
+    u32 left2 = off2 >= src2# ? 0 : src2# - off2;
+    u32 len1 = len > left1 ? left1 : len;
+    u32 len2 = len > left2 ? left2 : len;
     u32 max = len1 > len2 ? len2 : len1;
-    for( int i=0; i<max; i++ )
+    for( u32 i=0; i<max; i++ )
         if( src1[off1+i] != src2[off2+i] )
             return src1[off1+i] - src2[off2+i]; // Bytes determine compare
     return len1 - len2;                         // Length determines compare
diff --git a/chapter30/src/main/smp/sys/aryi64.smp b/chapter30/src/main/smp/sys/aryi64.smp
index 98b72605..b9f1fbed 100644
--- a/chapter30/src/main/smp/sys/aryi64.smp
+++ b/chapter30/src/main/smp/sys/aryi64.smp
@@ -9,36 +9,36 @@ struct aryi64 {
     };
 
     // Grow as needed
-    val _grow = { int len2 ->
-        if( len+len2 < buf# ) return self;
-        int newlen = buf# * 2;
-        while( len+len2 >= newlen ) newlen *= 2;
+    val _grow = { u32 len2 ->
+        if( len+len2 <= buf# ) return self;
+        u32 newlen = ary.capacity(buf#,len+len2);
+        if( !newlen ) libc._exit(1); // Length exceeds the array representation.
         i64[] !buf2 = new i64[newlen];
-        for( int i=0; i<buf#; i++ )
+        for( u32 i=0; i<len; i++ )
             buf2[i] = buf[i];
         buf = buf2;
         self;
     };
 
-    // Add a i64 to aryu8
+    // Add an i64 to aryi64
     val add = { i64 c ->
         _grow(1).buf[len++] = c;
         self;
     };
 
-    val get = { int index -> return buf[index]; };
+    val get = { u32 index -> return buf[index]; };
 
     // Write the bracketed array-list form to aryu8.
     val str = { ->
         // TODO: clunky default constructor syntax
         var str = new aryu8().add('[');
-        for( int i=0; i<len; i++ )
+        for( u32 i=0; i<len; i++ )
             str.num(buf[i]).add(',').add(' ');
         if( len ) str.undo(2);
         return str.add(']');
     };
 
-    val swap = { int i, int j ->
+    val swap = { u32 i, u32 j ->
         i64 tmp = buf[i];
         buf[i] = buf[j];
         buf[j] = tmp;
@@ -75,8 +75,11 @@ val parseAryI64 = { u8[~] str ->
     return s.x == s.buf# ? nums : null;
 };
 
-val copy = { i64[] dst, int doff, i64[~] src, int soff, int len ->
-    for( int i=0; i<len; i++ )
+val copy = { i64[] dst, u32 doff, i64[~] src, u32 soff, u32 len ->
+    if( doff > dst# || soff > src# ) return dst;
+    if( len > dst# - doff ) len = dst# - doff;
+    if( len > src# - soff ) len = src# - soff;
+    for( u32 i=0; i<len; i++ )
         dst[i+doff] = src[i+soff];
     return dst;
 };
diff --git a/chapter30/src/main/smp/sys/aryu8.smp b/chapter30/src/main/smp/sys/aryu8.smp
index 21cf920b..18543f13 100644
--- a/chapter30/src/main/smp/sys/aryu8.smp
+++ b/chapter30/src/main/smp/sys/aryu8.smp
@@ -7,12 +7,12 @@ struct aryu8 {
     new aryu8 = { -> buf = new u8[1]; };
 
     // Grow as needed
-    val _grow = { int len2 ->
-        if( len+len2 < buf# ) return self;
-        int newlen = buf# * 2;
-        while( len+len2 >= newlen ) newlen *= 2;
+    val _grow = { u32 len2 ->
+        if( len+len2 <= buf# ) return self;
+        u32 newlen = ary.capacity(buf#,len+len2);
+        if( !newlen ) libc._exit(1); // Length exceeds the array representation.
         u8[] !buf2 = new u8[newlen];
-        ary.copy(buf2,0,buf,0,buf#);
+        ary.copy(buf2,0,buf,0,len);
         buf = buf2;
         self;
     };
@@ -27,38 +27,28 @@ struct aryu8 {
 
     // Add all of a plain array to the aryu8
     val addAry = { u8[~] xs ->
-        _grow(xs#);
-        ary.copy(buf,len,xs,0,xs#);
-        len += xs#;
+        u32 n=xs#;
+        _grow(n);
+        ary.copy(buf,len,xs,0,n);
+        len += n;
         self;
     };
 
     // Remove x bytes from the tail.
-    val undo = { int x ->
+    val undo = { u32 x ->
         len = len >= x ? len-x : 0;
         self;
     };
 
     // Print ASCII number into aryu8
     val num = { i64 x ->
-        if( !x ) { add('0'); return self; }
-        if( x < 0 ) { add('-'); x = -x; }
-        i64 ten = 1, log = 0;
-        while( ten <= x ) { ten *= 10; log++; }
-        for( int i=0; i<log; i++ ) {
-            ten /= 10;
-            i64 q = x/ten;
-            u8 digit = q+'0';
-            add(digit);
-            x -= q*ten;
-        }
+        text.integer(self,x,0,0,-1);
         self;
     };
 
-    // Write to fd, returns the number of bytes written (len).
+    // Write all bytes to fd; return len, or -1 with errno set on failure.
     val write = { i32 fd ->
-        i64 ptr = buf; // Cast buffer pointer to i64 for native C call
-        libc.write(fd,ptr,len);
+        io.writeOff(fd,buf,0,len);
     };
 };
 
@@ -66,7 +56,7 @@ struct aryu8 {
 // Parse one integer, ignore trailing data; returns 0 with an empty string.
 // If you want a more robust parsing, use the `scan` class
 val atoi = { u8[~] str ->
-    int x = 0;
+    u32 x = 0;
     while( x < str# && str[x] <= ' ' ) x++;
     if( x == str# ) return 0;
     bool neg = false;
@@ -77,11 +67,12 @@ val atoi = { u8[~] str ->
     return neg ? -n : n;
 };
 
-// Zero-terminate string for libc strings.  No error checking, just copies and
-// appends a zero.
+// Zero-terminate a string for libc, reserving one array element for the zero.
 { u8[~] -> u8[] } str0 = { u8[~] str ->
+  if( str# == 4294967295 ) libc._exit(1);
   u8[] !strz = new u8[str#+1];
-  ary.copy(strz,0,str,0,str#);
+  u32 len=str#;
+  ary.copy(strz,0,str,0,len);
   strz[str#] = '\0';
   strz;
 };
diff --git a/chapter30/src/main/smp/sys/io.smp b/chapter30/src/main/smp/sys/io.smp
index d6263ffe..14993429 100644
--- a/chapter30/src/main/smp/sys/io.smp
+++ b/chapter30/src/main/smp/sys/io.smp
@@ -4,43 +4,74 @@
 // Write byte array to stdout
 val p          = { u8[~] str -> write(1,str); };
 val p_noInline = { u8[~] str -> write(1,str); };
+// Write to stderr
+val err = { u8[~] str -> write(libc.STDERR,str); };
 
-// Return fd contents as a u8[].
+
+// Read until EOF, including after short reads.  Return an empty array for an
+// empty stream, or null on error with errno preserved (partial data discarded).
 val read = { i32 fd ->
-    var buf = new u8[8*1024];
-    i64 ptr = buf;
-    int len = 0;
+    val chunk = new u8[8*1024];
+    i64 ptr = chunk;
+    val buf = new aryu8();
     while( true ) {
-        i32 rez = libc.read(fd,ptr,buf#);
-        if( rez > buf# ) libc._exit(libc.errno());
-        len += rez;
-        if( rez < buf# )
-            break;
-        libc._exit(-2); // Need to implement for more than 8K input
+        i64 rez = libc.read(fd,ptr,chunk#);
+        if( rez < 0 ) {
+            if( libc.errno() == libc.EINTR ) continue;
+            return null;
+        }
+        if( rez == 0 ) break;
+        if( buf.len+rez > 4294967295 ) {
+            libc.set_errno(libc.EOVERFLOW);
+            return null;
+        }
+        u32 count = rez;
+        buf._grow(count);
+        ary.copy(buf.buf,buf.len,chunk,0,count);
+        buf.len += count;
     }
-    var out = new u8[len];
-    ary.copy(out,0,buf,0,len);
+    val out = new u8[buf.len];
+    return ary.copy(out,0,buf.buf,0,buf.len);
 };
 
-// Write all of str to fd.
+// Write all bytes, returning the count or -1 with errno set. An error can
+// follow a successfully written prefix; it does not undo that prefix.
 val write = { i32 fd, u8[~] str ->
-  i64 ptr = str;                // Convert array pointer to a i64 for the native call
-  libc.write(fd,ptr,str#);
+    writeOff(fd,str,0,str#);
 };
 
-// Write all of str to fd.
+// Write a slice, capping len at the remaining bytes.  An offset past the end
+// is invalid, including for an empty write.  A valid empty slice returns zero.
+// Invalid arguments return -1;
 val writeOff = { i32 fd, u8[~] str, u32 off, u32 len ->
-  i64 ptr = str;                // Convert array pointer to a i64 for the native call
-  ptr += off;                   // Skip offset
-  // Cap at available length
-  if( len > str# - off ) len = str# - off;
-  // Do the write
-  libc.write(fd,ptr,len);
+    if( off > str# ) return libc.set_errno(libc.EINVAL);
+    if( len > str# - off ) len = str# - off;
+    i64 ptr = str;
+    ptr += off;
+    i64 done = 0;
+    while( done < len ) {
+        i64 rez = libc.write(fd,ptr+done,len-done);
+        if( rez < 0 ) {
+            if( libc.errno() == libc.EINTR ) continue;
+            return -1;
+        }
+        if( rez == 0 ) {
+            libc.set_errno(libc.EIO);
+            return -1;
+        }
+        done += rez;
+    }
+    return done;
 };
 
 // Return stdin as a u8[].
 val stdin = { -> read(0); };
 
+// One byte, without Enter or echo. Restores the previous terminal mode before
+// returning. Files/pipes also work. Returns 0..255, or -1 with libc.errno() set
+// to libc.EOF or an OS error. Ctrl-C is byte 3; escape/UTF-8 sequences are multiple bytes.
+val getch = { -> libc.simple_getch(); };
+
 // Create file for writing.  Return fd, or -1 and errno has the error code
 val create = { u8[~] str ->
     i64 ptr = sys.aryu8.str0(str);
diff --git a/chapter30/src/main/smp/sys/libc.smp b/chapter30/src/main/smp/sys/libc.smp
index 17ee65cb..7122bbd8 100644
--- a/chapter30/src/main/smp/sys/libc.smp
+++ b/chapter30/src/main/smp/sys/libc.smp
@@ -2,17 +2,17 @@
 // libc bindings:
 //   https://www.man7.org/linux/man-pages/man2/<libc call>.2.html
 
-// The buffers are int-versions of zero-terminated strings.
-//     int buf = aryu8.str0("some_file");
+// The buffers are i64 addresses of zero-terminated strings.
+//     i64 buf = aryu8.str0("some_file");
 // buf mode perm-> fd
 {  i64 i32  i32 -> i32 } open = "C";
 // buf perm -> fd
 {  i64 i32 -> i32 } creat = "C";
 
 // fd  buf len -> len
-{  i32 i64 u32 -> i32 } write = "C";
+{  i32 i64 i64 -> i64 } write = "C";
 // fd  buf len -> len
-{  i32 i64 u32 -> i32 } read = "C";
+{  i32 i64 i64 -> i64 } read = "C";
 // fd  -> err
 {  i32 -> i32 } close = "C";
 // path -> err
@@ -27,12 +27,29 @@ i32 O_TRUNC = 1024; // 04000 on x86_64-pc-cygwin
 i32 STDIN  = 0;
 i32 STDOUT = 1;
 i32 STDERR = 2;
+i32 EOF    = -1; // simple_getch sets errno to EOF on end-of-input.
 
 // status
 {  i32 -> i32 } _exit = "C";
+
 // errno is not an ordinary C data symbol; read it through the native runtime.
 { i32 } simple_errno = "C";
 val errno = { -> simple_errno(); };
+{ i32 -> i32 } simple_set_errno = "C";
+// Set errno and return -1, matching the native I/O error convention.
+val set_errno = { i32 error -> simple_set_errno(error); };
+
+i32 EINTR = "C";
+i32 EIO = "C";
+i32 EINVAL = "C";
+i32 EOVERFLOW = "C";
+
+// Read one byte from stdin, without <enter> or echo.  Restores the previous
+// terminal mode before returning.  Files and pipes also work.  Returns 0..255,
+// or -1 with errno set to EOF or an OS error.  Ctrl-C is byte 3; escape/UTF-8
+// sequences are multiple bytes.
+{ i32 } simple_getch = "C";
+
 // addr len prot flags fd  off -> void*
 {  i64  i64 i32  i32   i32 i32 -> i64 } mmap = "C";
 // mmap flags
diff --git a/chapter30/src/main/smp/sys/rt.smp b/chapter30/src/main/smp/sys/rt.smp
new file mode 100644
index 00000000..d62b4def
--- /dev/null
+++ b/chapter30/src/main/smp/sys/rt.smp
@@ -0,0 +1,3 @@
+// Run Time support: "rt" has the same meaning as Java's rt.jar or C's crt.o.
+// Native entry helpers are compiled and linked independently of ordinary sys
+// imports, so programs without library imports can use the same startup code.
diff --git a/chapter30/src/main/smp/sys/rt/simple_args.smp b/chapter30/src/main/smp/sys/rt/simple_args.smp
new file mode 100644
index 00000000..3f630e54
--- /dev/null
+++ b/chapter30/src/main/smp/sys/rt/simple_args.smp
@@ -0,0 +1,22 @@
+// Native startup support, compiled independently and linked with the CRT.
+// Raw native addresses stay i64; only the arrays allocated here are Simple objects.
+{ i64 i64 -> i64 } simple_argv = "C";
+{ i64 -> i64 } strlen = "C";
+{ i64 i64 i64 -> i64 } memcpy = "C";
+
+val simple_args = { i64 argc, i64 argv ->
+    if( argc < 0 || argc > 4294967295 ) return null;
+    // Zero-filled reference arrays require nullable elements. Every slot is
+    // filled before returning; the native entry bridge publishes u8[~][].
+    val args = new u8[~]?[argc];
+    for( i64 i=0; i<argc; i++ ) {
+        i64 src = simple_argv(argv,i);
+        i64 len = strlen(src);
+        if( len < 0 || len > 4294967295 ) return null;
+        val bytes = new u8[len];
+        i64 dst = bytes;
+        memcpy(dst,src,len);
+        args[i] = bytes;
+    }
+    return args;
+};
diff --git a/chapter30/src/main/smp/sys/text.smp b/chapter30/src/main/smp/sys/text.smp
new file mode 100644
index 00000000..a414ff45
--- /dev/null
+++ b/chapter30/src/main/smp/sys/text.smp
@@ -0,0 +1,98 @@
+// Formatting primitives used directly by interpolation and named converters.
+// Keep this module free of interpolation: sys can build itself from source.
+// spec's low byte is the format kind; bits 8..12 are flags: - + space # 0.
+
+val begin = { -> new aryu8(); };
+
+val end = { aryu8 b ->
+    val bytes = new u8[b.len];
+    ary.copy(bytes,0,b.buf,0,b.len);
+    u8[~] result = bytes;
+    result;
+};
+
+val _pad = { !aryu8 b, i64 n, u8 c ->
+    for( i64 i=0; i<n; i++ ) b.add(c);
+    b;
+};
+
+val string = { !aryu8 b, u8[~] s, i64 spec, i64 width, i64 precision ->
+    i64 len=s#;
+    if( precision>=0 && precision<len ) len=precision;
+    i64 pad=width-len;
+    if( !(spec&256) ) _pad(b,pad,' ');
+    for( i64 i=0; i<len; i++ ) b.add(s[i]);
+    if( spec&256 ) _pad(b,pad,' ');
+    b;
+};
+
+val integer = { !aryu8 b, i64 value, i64 spec, i64 width, i64 precision ->
+    i64 kind=spec&255;
+    if( kind=='b' ) return string(b,value ? "true" : "false",spec,width,-1);
+    if( kind=='c' ) {
+        if( !(spec&256) ) _pad(b,width-1,' ');
+        u8 c=value;
+        b.add(c);
+        if( spec&256 ) _pad(b,width-1,' ');
+        return b;
+    }
+    bool signed=kind==0 || kind=='d' || kind=='i';
+    i64 base=kind=='o' ? 8 : (kind=='x' || kind=='X' ? 16 : 10);
+    u8[~] alphabet=kind=='X' ? "0123456789ABCDEF" : "0123456789abcdef";
+    val digits=new u8[22]; // Maximum: 22 octal digits for a 64-bit integer.
+    i64 count=0, n=value;
+    // Signed decimal stays nonpositive, including the minimum i64.
+    if( signed && n>0 ) n=-n;
+    if( n==0 && precision!=0 ) digits[count++]='0';
+    while( n!=0 ) {
+        i64 q=0, r=0;
+        if( signed ) { q=n/base; r=q*base-n; }
+        else {
+            // Unsigned division without a u64 type. Halving first makes
+            // the dividend nonnegative; the remainder needs at most one fix.
+            q=((n>>>1)/base)*2;
+            r=n-q*base;
+            if( r>=base ) { q++; r-=base; }
+        }
+        digits[count++]=alphabet[r];
+        n=q;
+    }
+    u8[~] !prefix="";
+    if( signed ) {
+        if( value<0 ) prefix="-";
+        else if( spec&512 ) prefix="+";
+        else if( spec&1024 ) prefix=" ";
+    } else if( (spec&2048) && value!=0 ) {
+        if( kind=='x' ) prefix="0x";
+        if( kind=='X' ) prefix="0X";
+    }
+    i64 zeros=precision>count ? precision-count : 0;
+    // Alternate octal always begins with a zero, including precision-zero 0.
+    if( kind=='o' && (spec&2048) && zeros==0 && (count==0 || digits[count-1]!='0') ) zeros=1;
+    i64 pad=width-prefix#-zeros-count;
+    bool left=(spec&256)!=0;
+    bool zero=(spec&4096)!=0 && precision<0 && !left;
+    if( !left && !zero ) _pad(b,pad,' ');
+    b.addAry(prefix);
+    if( zero ) _pad(b,pad,'0');
+    _pad(b,zeros,'0');
+    while( count>0 ) b.add(digits[--count]);
+    if( left ) _pad(b,pad,' ');
+    b;
+};
+
+// Only conversion of binary floating-point values is delegated to libc.
+// The fixed signature accepts a validated format and returns a byte string.
+{ f64 i64 i64 i64 -> u8[~] } simple_text_float = "C";
+val floating = { !aryu8 b, f64 value, i64 spec, i64 width, i64 precision ->
+    b.addAry(simple_text_float(value,spec,width,precision));
+};
+
+// Explicitly named, typed conversions share the same formatting routines.
+val int  = { i64  x -> end(integer (begin(),x, 0 ,0,-1)); };
+val flt  = { f64  x -> end(floating(begin(),x, 0 ,0,-1)); };
+val f32  = { f32  x -> end(floating(begin(),x,'g',0,-1)); };
+val f64  = { f64  x -> end(floating(begin(),x, 0 ,0,-1)); };
+val char = { i64  x -> end(integer (begin(),x,'c',0,-1)); };
+val bool = { bool x -> end(integer (begin(),x,'b',0,-1)); };
+val hex  = { i64  x -> end(integer (begin(),x,'x',0,-1)); };
-- 
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