Allow oper-assign, += -= etc

3 files changed, 64 insertions, 21 deletions

diff --git a/chapter17/README.md b/chapter17/README.md
index 1bac940b..d65ff879 100644
--- a/chapter17/README.md
+++ b/chapter17/README.md
@@ -12,6 +12,14 @@ Also allows `s.fld++` and `ary[idx]++`, and their `--` variants.
 Allow pre-increment for identifiers only, for now: `--pc`.
 
 
+## Operator assignment
+
+Along the same lines as post-increment, we now allow `op=` assignment
+with semantics similar to other languages.
+
+`x += y`
+
+
 ## var & val
 
 `var` can be used in the `type` position to indicate a "variable" (mutable
@@ -125,11 +133,5 @@ return i; // ERROR: Undefined name 'i'
 
 
 
-oper-assign +=, -=
 TODO
 switch
-
-
-
-
-
diff --git a/chapter17/src/main/java/com/seaofnodes/simple/Parser.java b/chapter17/src/main/java/com/seaofnodes/simple/Parser.java
index 09ea21ac..47e7c3bb 100644
--- a/chapter17/src/main/java/com/seaofnodes/simple/Parser.java
+++ b/chapter17/src/main/java/com/seaofnodes/simple/Parser.java
@@ -889,13 +889,30 @@ public class Parser {
         if( matchx("new"  ) ) return alloc();
         // Expect an identifier now
         ScopeMinNode.Var n = requireLookupId("an identifier or expression");
-        Node rvalue = _scope.in(n).keep();
-        if( matchx("++") || matchx("--") ) {
-            if( n._final )
-                throw error("Cannot reassign final '"+n._name+"'");
-            _scope.update(n,zsMask(peep(new AddNode(rvalue,con( _lexer.peek(-1)=='+' ? 1 : -1))),n.type()));
-        }
-        return rvalue.unkeep();
+        Node rvalue = _scope.in(n);
+        // Check for assign-update, x += e0;
+        char ch = _lexer.matchOperAssign();
+        if( ch==0  ) return rvalue;
+        if( n._final )
+            throw error("Cannot reassign final '"+n._name+"'");
+        Node op = switch(ch) {
+        case '+'      -> new AddNode(rvalue,null);
+        case '-'      -> new SubNode(rvalue,null);
+        case '*'      -> new MulNode(rvalue,null);
+        case '/'      -> new DivNode(rvalue,null);
+        case        1 -> new AddNode(rvalue,con( 1));
+        case (char)-1 -> new AddNode(rvalue,con(-1));
+        default -> throw Utils.TODO();
+        };
+        // Return pre-value (x+=1) or post-value (x++)
+        boolean pre = op.in(2)==null;
+        // Parse RHS argument as needed
+        if( pre )
+            { op.keep().setDef(2,parseExpression());  op.unkeep(); }
+        else rvalue.keep();     // Keep post-value across peeps
+        op = zsMask(peep(op),n.type());
+        _scope.update(n,op);
+        return pre ? op : rvalue.unkeep();
     }
 
     ScopeMinNode.Var requireLookupId(String msg) {
@@ -1344,12 +1361,28 @@ public class Parser {
 
         //
         private boolean isPunctuation(char ch) {
-            return "=;[]<>()+-/*".indexOf(ch) != -1;
+            return "=;[]<>()+-/*&|^".indexOf(ch) != -1;
         }
 
         private String parsePunctuation() {
             int start = _position;
             return new String(_input, start, 1);
         }
+
+        // Next oper= character, or 0.
+        // As a convenience, mark "++" as a char 1 and "--" as char -1 (65535)
+        public char matchOperAssign() {
+            skipWhiteSpace();
+            if( _position+2 >= _input.length ) return 0;
+            char ch0 = (char)_input[_position];
+            if( "+-/*&|^".indexOf(ch0) == -1 ) return 0;
+            char ch1 = (char)_input[_position+1];
+            if( ch1=='=' )
+                { _position += 2; return ch0; }
+            if( isIdLetter((char)_input[_position+2]) ) return 0; // Stop --x
+            if( ch0 == '+' && ch1 == '+' ) { _position += 2; return (char) 1; }
+            if( ch0 == '-' && ch1 == '-' ) { _position += 2; return (char)-1; }
+            return 0;
+        }
     }
 }
diff --git a/chapter17/src/test/java/com/seaofnodes/simple/Chapter17Test.java b/chapter17/src/test/java/com/seaofnodes/simple/Chapter17Test.java
index b1f7eb43..176a9236 100644
--- a/chapter17/src/test/java/com/seaofnodes/simple/Chapter17Test.java
+++ b/chapter17/src/test/java/com/seaofnodes/simple/Chapter17Test.java
@@ -105,6 +105,14 @@ return s.x;
         assertEquals(255L, Evaluator.evaluate(stop, 0));
     }
 
+    @Test
+    public void testInc8() {
+        Parser parser = new Parser("int x; x+=2; return x+=3;");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 5;", stop.toString());
+        assertEquals(5L, Evaluator.evaluate(stop, 0));
+    }
+
     // ---------------------------------------------------------------
     @Test public void testVar0() {
         Parser parser = new Parser("var d; return d;");
@@ -288,7 +296,7 @@ return b ? b.next ? b.next.x : b.x; // parses "b ? (b.next ? b.next.x : b.x) : 0
         Parser parser = new Parser("""
 int sum=0;
 for( int i=0; i<arg; i++ )
-    sum = sum + i;
+    sum += i;
 return sum;
 """);
         StopNode stop = parser.parse().iterate();
@@ -301,7 +309,7 @@ return sum;
         Parser parser = new Parser("""
 int sum=0, i=0;
 for( ; i<arg; i++ )
-    sum = sum + i;
+    sum += i;
 return sum;
 """);
         StopNode stop = parser.parse().iterate();
@@ -315,7 +323,7 @@ return sum;
 int sum=0;
 for( int i=0; ; i++ ) {
     if( i>=arg ) break;
-    sum = sum + i;
+    sum += i;
 }
 return sum;
 """);
@@ -329,7 +337,7 @@ return sum;
         Parser parser = new Parser("""
 int sum=0;
 for( int i=0; i<arg; )
-    sum = sum + i++;
+    sum += i++;
 return sum;
 """);
         StopNode stop = parser.parse().iterate();
@@ -342,7 +350,7 @@ return sum;
         Parser parser = new Parser("""
 int sum=0;
 for( int i=0; i<arg; i++ )
-    sum = sum + i;
+    sum += i;
 return i;
 """);
         try { parser.parse().iterate(); fail(); }
@@ -361,7 +369,7 @@ while( arg-- )
 int sum=0;
 var ptr = head; // A read-only ptr, to be assigned from read-only next fields
 for( ; ptr; ptr = ptr.next )
-    sum = sum + ptr.i;
+    sum += ptr.i;
 return sum;
 """);
         StopNode stop = parser.parse().iterate();
@@ -382,7 +390,7 @@ for( p=2; p*p < arg; p++ ) {
     // p is now a prime
     primes[nprimes++] = p;
     // Mark out the rest non-primes
-    for( int i = p + p; i < ary#; i = i + p )
+    for( int i = p + p; i < ary#; i += p )
         ary[i] = true;
 }
 // Now just collect the remaining primes, no more marking