Chapter 6 (#38)

* #37 Create chapter 6 skeleton

* #37 Revise type system - TOP, BOTTOM, CONTROL are now directly implemented in Type, XCONTROL is a new type and that's implemented directly too.
We have a _type field that is like an enum.

* #37 Revise Type.meet() - this is now final.
Subclasses can override xmeet() which is protected but
now handles simple types in Type itself.

* #37 Basic test for peephole of CFG

* #37 Revise compute of if

* #37 Revise compute of if

* #37 WIP peephole of If

* #37 WIP peephole of If

* #37 WIP peephole of If

* #37 WIP peephole of If

* #37 WIP peephole of If

* #37 WIP fix the chars inserted by IntelliJ

* #37 WIP Fix compute type in IfNode

* #37 WIP Null check region inputs

* #37 WIP Fix where we choose great grand parent instead of grand parent
Add new test

* #37 WIP More fixes and tests

* #37 WIP Some minor adjustments

* Cleanup folding dead IF tests

Remove isDeadCtrl & just test for the constant.
Remove DEAD_CTRL, doesn't properly reset between tests.
Move keep/unkeep to Node.
PhiNode has a proper compute() call.
ProjNode ideal is a lot simpler.
Region doesn't ever get a null.
Move the mergeScopes Region peep till after all Phis are added.
Type TOP and XCONTROL count as constants.
TypeTuple gets a toString

* #37 WIP Upate README

* #37 WIP Region node should check if one of its inputs is a region that needs to be peepholed

* #37 WIP If node should check if its ctrl input is a Region that has only 1 live input so can be peepholed

* #37 WIP Further update to README to make the peephole logic clearer. Also discuss the relationship between Region and Phi nodes

* Region removes dead input paths

Remove region-folding in Return, If.
Add a Makefile.
Reformat triple-quote lines to be emacs-friendly.

* StopNode idealize

Return type sharpens to include control input.

* Remove !=, >=, >; use Not and <, <=, ==

Fix bug mixing rotating different ops.
Generalize Add fold constants; apply to Mul, EQ.
Fix Div.copy

* Fix bug rotating e.g. < or <=

Peep is only valid for associative ops

* #37 WIP Doc updates

* Work over the Ch6 Readme

Major issue: Region inputs align 1-to-1 with Phi inputs, but a Region can have zero to many Phis.  When we lose a Region input (dead path), we need to lose the same inputs to each Phi - but we don't lose the Phis themselves, unless we're folding away down to the last live input.

* Update chapter06/README.md

Co-authored-by: Yichen Yan <oraluben@outlook.com>

* Update chapter06/README.md

Co-authored-by: Yichen Yan <oraluben@outlook.com>

* #37 Backport type system changes to chapter 2

* #37 Backport type system changes to chapter 3

* #37 Backport type system changes to chapter 4

* #37 Backport type system changes to chapter 5

* #37 Merge chapter 5 updates from main.
Remove language grammar module as we describe the grammar incrementally in each chapter.

* #37 Chapter 6 doc updates - added visuals to show effects of CFG peephole

* #37 Sync some updates to chapter 2

* #37 Sync some updates to chapter 3

* #37 Sync some updates to chapter 4

---------

Co-authored-by: Cliff Click <cliffc@acm.org>
Co-authored-by: Yichen Yan <oraluben@outlook.com>

1 files changed, 795 insertions, 0 deletions

diff --git a/chapter06/src/test/java/com/seaofnodes/simple/Chapter06Test.java b/chapter06/src/test/java/com/seaofnodes/simple/Chapter06Test.java
new file mode 100644
index 00000000..801f8d3f
--- /dev/null
+++ b/chapter06/src/test/java/com/seaofnodes/simple/Chapter06Test.java
@@ -0,0 +1,795 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter06Test {
+
+    @Test
+    public void testChapter6PeepholeReturn() {
+        Parser parser = new Parser(
+"""
+if( true ) return 2;
+return 1;
+""");
+        StopNode stop = parser.parse(true);
+        assertEquals("return 2;", stop.toString());
+        assertTrue(stop.ret().ctrl() instanceof ProjNode);
+    }
+
+    @Test
+    public void testChapter6PeepholeRotate() {
+        Parser parser = new Parser(
+"""
+int a = 1;
+if (arg)
+    a = 2;
+return (arg < a) < 3;
+""");
+        StopNode stop = parser.parse(false);
+        assertEquals("return ((arg<Phi(Region12,2,1))<3);", stop.toString());
+    }
+
+    @Test
+    public void testChapter6PeepholeCFG() {
+        Parser parser = new Parser(
+"""
+int a=1;
+if( true )
+  a=2;
+else
+  a=3;
+return a;
+""");
+        StopNode stop = parser.parse(true);
+        assertEquals("return 2;", stop.toString());
+        assertTrue(stop.ret().ctrl() instanceof ProjNode);
+    }
+
+    @Test
+    public void testChapter6IfIf() {
+        Parser parser = new Parser(
+"""
+int a=1;
+if( arg!=1 )
+    a=2;
+else
+    a=3;
+int b=4;
+if( a==2 )
+    b=42;
+else
+    b=5;
+return b;""", TypeInteger.BOT);
+        StopNode stop = parser.parse(true);
+        assertEquals("return Phi(Region32,42,5);", stop.toString());
+    }
+
+    @Test
+    public void testChapter6IfArgIf() {
+        Parser parser = new Parser(
+"""
+int a=1;
+if( 1==1 )
+    a=2;
+else
+    a=3;
+int b=4;
+if( arg==2 )
+    b=a;
+else
+    b=5;
+return b;""", TypeInteger.BOT);
+        StopNode stop = parser.parse(true);
+        assertEquals("return Phi(Region28,2,5);", stop.toString());
+    }
+
+    @Test
+    public void testChapter6Merge3With2() {
+        Parser parser = new Parser(
+"""
+int a=1;
+if( arg==1 )
+    if( arg==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+#showGraph;""", TypeInteger.constant(2));
+        StopNode stop = parser.parse();
+        assertEquals("return 5;", stop.toString());
+    }
+
+    @Test
+    public void testChapter6Merge3With1() {
+        Parser parser = new Parser(
+"""
+int a=1;
+if( arg==1 )
+    if( arg==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.constant(1));
+        StopNode stop = parser.parse(true);
+        assertEquals("return 3;", stop.toString());
+    }
+
+    @Test
+    public void testChapter6Merge3Peephole() {
+        Parser parser = new Parser(
+"""
+int a=1;
+if( arg==1 )
+    if( 1==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.BOT);
+        StopNode stop = parser.parse(true);
+        assertEquals("return Phi(Region36,3,Phi(Region34,4,5));", stop.toString());
+    }
+
+    @Test
+    public void testChapter6Merge3Peephole1() {
+        Parser parser = new Parser(
+"""
+int a=1;
+if( arg==1 )
+    if( 1==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.constant(1));
+        StopNode stop = parser.parse(true);
+        assertEquals("return 3;", stop.toString());
+    }
+
+    @Test
+    public void testChapter6Merge3Peephole3() {
+        Parser parser = new Parser(
+"""
+int a=1;
+if( arg==1 )
+    if( 1==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.constant(3));
+        StopNode stop = parser.parse(true);
+        assertEquals("return 4;", stop.toString());
+    }
+
+    @Test
+    public void testChapter6Demo1NonConst() {
+        Parser parser = new Parser("""
+int a = 0;
+int b = 1;
+if( arg ) {
+    a = 2;
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b;
+""");
+        StopNode ret = parser.parse(true);
+        assertEquals("return (Phi(Region21,Phi(Region19,2,3),1)+Phi(Region21,2,0));", ret.toString());
+    }
+
+
+    @Test
+    public void testChapter6Demo1True() {
+        Parser parser = new Parser("""
+int a = 0;
+int b = 1;
+if( arg ) {
+    a = 2;
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b;
+""", TypeInteger.constant(1));
+        StopNode ret = parser.parse(true);
+        assertEquals("return 4;", ret.toString());
+    }
+
+    @Test
+    public void testChapter6Demo1False() {
+        Parser parser = new Parser("""
+int a = 0;
+int b = 1;
+if( arg ) {
+    a = 2;
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b;
+""", TypeInteger.constant(0));
+        StopNode ret = parser.parse(true);
+        assertEquals("return 1;", ret.toString());
+    }
+
+    @Test
+    public void testChapter6Demo2NonConst() {
+        Parser parser = new Parser("""
+int a = 0;
+int b = 1;
+int c = 0;
+if( arg ) {
+    a = 1;
+    if( arg==2 ) { c=2; } else { c=3; }
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b+c;
+""");
+        StopNode ret = parser.parse(true);
+        assertEquals("return ((Phi(Region32,Phi(Region22,2,3),0)+Phi(Region32,Phi(Region30,2,3),1))+Phi(Region32,1,0));", ret.toString());
+    }
+
+
+    @Test
+    public void testChapter6Demo2True() {
+        Parser parser = new Parser("""
+int a = 0;
+int b = 1;
+int c = 0;
+if( arg ) {
+    a = 1;
+    if( arg==2 ) { c=2; } else { c=3; }
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b+c;
+""", TypeInteger.constant(1));
+        StopNode ret = parser.parse(true);
+        assertEquals("return 6;", ret.toString());
+    }
+
+    @Test
+    public void testChapter6Demo2arg2() {
+        Parser parser = new Parser("""
+int a = 0;
+int b = 1;
+int c = 0;
+if( arg ) {
+    a = 1;
+    if( arg==2 ) { c=2; } else { c=3; }
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b+c;
+""", TypeInteger.constant(2));
+        StopNode ret = parser.parse(true);
+        assertEquals("return 5;", ret.toString());
+    }
+
+
+
+    @Test
+    public void testChapter5IfStmt() {
+        Parser parser = new Parser(
+"""
+int a = 1;
+if (arg == 1)
+    a = arg+2;
+else {
+    a = arg-3;
+    #showGraph;
+}
+#showGraph;
+return a;""");
+        StopNode ret = parser.parse(true);
+        assertEquals("return Phi(Region17,(arg+2),(arg-3));", ret.toString());
+    }
+  
+    @Test
+    public void testChapter5Test() {
+        Parser parser = new Parser(
+"""
+int c = 3;
+int b = 2;
+if (arg == 1) {
+    b = 3;
+    c = 4;
+}
+return c;""", TypeInteger.BOT);
+        StopNode ret = parser.parse(true);
+        assertEquals("return Phi(Region16,4,3);", ret.toString());
+    }
+    
+    @Test
+    public void testChapter5Return2() {
+        Parser parser = new Parser(
+"""
+if( arg==1 ) 
+    return 3; 
+else 
+    return 4; 
+#showGraph;""", TypeInteger.BOT);
+        StopNode stop = parser.parse();
+        assertEquals("Stop[ return 3; return 4; ]", stop.toString());
+    }
+    
+    @Test
+    public void testChapter5IfMergeB() {
+        Parser parser = new Parser(
+"""
+int a=arg+1;
+int b=0;
+if( arg==1 )
+    b=a;
+else
+    b=a+1;
+return a+b;""");
+        StopNode ret = parser.parse(true);
+        assertEquals("return ((arg*2)+Phi(Region20,2,3));", ret.toString());
+    }
+
+    @Test
+    public void testChapter5IfMerge2() {
+        Parser parser = new Parser(
+"""
+int a=arg+1;
+int b=arg+2;
+if( arg==1 )
+    b=b+a;
+else
+    a=b+1;
+return a+b;""");
+        StopNode ret = parser.parse(true);
+        assertEquals("return ((Phi(Region31,(arg*2),arg)+arg)+Phi(Region31,4,5));", ret.toString());
+    }
+
+    @Test
+    public void testChapter5Merge3() {
+        Parser parser = new Parser(
+"""
+int a=1;
+if( arg==1 )
+    if( arg==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+#showGraph;""", TypeInteger.BOT);
+        StopNode stop = parser.parse();
+        assertEquals("return Phi(Region33,Phi(Region21,2,3),Phi(Region31,4,5));", stop.toString());
+    }
+
+    @Test
+    public void testChapter5Merge4() {
+        Parser parser = new Parser(
+"""
+int a=0;
+int b=0;
+if( arg )
+    a=1;
+if( arg==0 )
+    b=2;
+return arg+a+b;
+#showGraph;""", TypeInteger.BOT);
+        StopNode stop = parser.parse();
+        assertEquals("return ((arg+Phi(Region13,1,0))+Phi(Region22,2,0));", stop.toString());
+    }
+
+    @Test
+    public void testChapter5Merge5() {
+        Parser parser = new Parser(
+"""
+int a=arg==2;
+if( arg==1 )
+{
+    a=arg==3;
+}
+return a;""");
+        StopNode ret = parser.parse(true);
+        assertEquals("return (arg==Phi(Region16,3,2));", ret.toString());
+    }
+
+    @Test
+    public void testChapter5True() {
+      StopNode stop = new Parser("return true;").parse();
+      assertEquals("return 1;",stop.toString());
+    }
+    
+    @Test
+    public void testChapter5HalfDef() {
+        try { 
+            new Parser("if( arg==1 ) int b=2; return b;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Cannot define a new name on one arm of an if",e.getMessage());
+        }
+    }
+    
+    @Test
+    public void testChapter5HalfDef2() {
+        try { 
+            new Parser("if( arg==1 ) { int b=2; } else { int b=3; } return b;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Undefined name 'b'",e.getMessage());
+        }
+    }
+    
+    @Test
+    public void testChapter5BadNum() {
+        try { 
+            new Parser("return 1-;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, expected an identifier or expression: ;",e.getMessage());
+        }
+    }
+      
+    @Test
+    public void testChapter5Keyword1() {
+        try { 
+            new Parser("int true=0; return true;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Expected an identifier, found 'true'",e.getMessage());
+        }
+    }
+      
+    @Test
+    public void testChapter5Keyword2() {
+        try { 
+            new Parser("int else=arg; if(else) else=2; else else=1; return else;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Expected an identifier, found 'else'",e.getMessage());
+        }
+    }
+
+    @Test
+        public void testChapter5Keyword3() {
+        try { 
+            new Parser("int a=1; ififif(arg)inta=2;return a;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, expected =: (",e.getMessage());
+        }
+    }
+    
+    @Test
+    public void testChapter4Peephole() {
+        Parser parser = new Parser("return 1+arg+2; #showGraph;");
+        StopNode ret = parser.parse();
+        assertEquals("return (arg+3);", ret.print());
+    }
+
+    @Test
+    public void testChapter4Peephole2() {
+        Parser parser = new Parser("return (1+arg)+2;");
+        StopNode ret = parser.parse();
+        assertEquals("return (arg+3);", ret.print());
+    }
+
+    @Test
+    public void testChapter4Add0() {
+        Parser parser = new Parser("return 0+arg;");
+        StopNode ret = parser.parse();
+        assertEquals("return arg;", ret.print());
+    }
+
+    @Test
+    public void testChapter4AddAddMul() {
+        Parser parser = new Parser("return arg+0+arg;");
+        StopNode ret = parser.parse();
+        assertEquals("return (arg*2);", ret.print());
+    }
+  
+    @Test
+    public void testChapter4Peephole3() {
+        Parser parser = new Parser("return 1+arg+2+arg+3; #showGraph;");
+        StopNode ret = parser.parse();
+        assertEquals("return ((arg*2)+6);", ret.print());
+    }
+
+    @Test
+    public void testChapter4Mul1() {
+        Parser parser = new Parser("return 1*arg;");
+        StopNode ret = parser.parse();
+        assertEquals("return arg;", ret.print());
+    }
+  
+    @Test
+    public void testChapter4VarArg() {
+        Parser parser = new Parser("return arg; #showGraph;");
+        StopNode stop = parser.parse();
+        ReturnNode ret = stop.ret();
+        assertTrue(ret.in(0) instanceof ProjNode);
+        assertTrue(ret.in(1) instanceof ProjNode);
+    }
+
+    @Test
+    public void testChapter4ConstantArg() {
+        Parser parser = new Parser("return arg; #showGraph;", TypeInteger.constant(2));
+        StopNode ret = parser.parse();
+        assertEquals("return 2;", ret.print());
+    }
+
+    @Test
+    public void testChapter4CompEq() {
+        Parser parser = new Parser("return 3==3; #showGraph;");
+        StopNode ret = parser.parse();
+        assertEquals("return 1;", ret.print());
+    }
+
+    @Test
+    public void testChapter4CompEq2() {
+        Parser parser = new Parser("return 3==4; #showGraph;");
+        StopNode ret = parser.parse();
+        assertEquals("return 0;", ret.print());
+    }
+
+    @Test
+    public void testChapter4CompNEq() {
+        Parser parser = new Parser("return 3!=3; #showGraph;");
+        StopNode ret = parser.parse();
+        assertEquals("return 0;", ret.print());
+    }
+
+    @Test
+    public void testChapter4CompNEq2() {
+        Parser parser = new Parser("return 3!=4; #showGraph;");
+        StopNode ret = parser.parse();
+        assertEquals("return 1;", ret.print());
+    }
+
+    @Test
+    public void testChapter4Bug1() {
+        Parser parser = new Parser("int a=arg+1; int b=a; b=1; return a+2; #showGraph;");
+        StopNode ret = parser.parse();
+        assertEquals("return (arg+3);", ret.print());
+    }
+
+    @Test
+    public void testChapter4Bug2() {
+        Parser parser = new Parser("int a=arg+1; a=a; return a; #showGraph;");
+        StopNode ret = parser.parse();
+        assertEquals("return (arg+1);", ret.print());
+    }
+
+    @Test
+    public void testChapter4Bug3() {
+        try { 
+            new Parser("inta=1; return a;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Undefined name 'inta'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testChapter4Bug4() {
+        Parser parser = new Parser("return -arg;");
+        StopNode ret = parser.parse();
+        assertEquals("return (-arg);", ret.print());
+    }
+    
+    @Test
+    public void testVarDecl() {
+        Parser parser = new Parser("int a=1; return a;");
+        StopNode ret = parser.parse();
+        assertEquals("return 1;", ret.print());
+    }
+
+    @Test
+    public void testVarAdd() {
+        Parser parser = new Parser("int a=1; int b=2; return a+b;");
+        StopNode ret = parser.parse();
+        assertEquals("return 3;", ret.print());
+    }
+
+    @Test
+    public void testVarScope() {
+        Parser parser = new Parser("int a=1; int b=2; int c=0; { int b=3; c=a+b; } return c;");
+        StopNode ret = parser.parse();
+        assertEquals("return 4;", ret.print());
+    }
+
+    @Test
+    public void testVarScopeNoPeephole() {
+        Node._disablePeephole = true;
+        Parser parser = new Parser("int a=1; int b=2; int c=0; { int b=3; c=a+b; #showGraph; } return c; #showGraph;");
+        StopNode ret = parser.parse();
+        Node._disablePeephole = false;
+        assertEquals("return (1+3);", ret.print());
+    }
+
+    @Test
+    public void testVarDist() {
+        Parser parser = new Parser("int x0=1; int y0=2; int x1=3; int y1=4; return (x0-x1)*(x0-x1) + (y0-y1)*(y0-y1); #showGraph;");
+        StopNode ret = parser.parse();
+        assertEquals("return 8;", ret.print());
+    }
+
+    @Test
+    public void testSelfAssign() {
+        try { 
+            new Parser("int a=a; return a;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Undefined name 'a'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testChapter2ParseGrammar() {
+        Node._disablePeephole = true; // disable peephole so we can observe full graph
+        Parser parser = new Parser("return 1+2*3+-5;");
+        StopNode ret = parser.parse();
+        assertEquals("return (1+((2*3)+(-5)));", ret.print());
+        GraphVisualizer gv = new GraphVisualizer();
+        System.out.println(gv.generateDotOutput(parser));
+        Node._disablePeephole = false;
+    }
+
+    @Test
+    public void testChapter2AddPeephole() {
+        Parser parser = new Parser("return 1+2;");
+        StopNode ret = parser.parse();
+        assertEquals("return 3;", ret.print());
+    }
+
+    @Test
+    public void testChapter2SubPeephole() {
+        Parser parser = new Parser("return 1-2;");
+        StopNode ret = parser.parse();
+        assertEquals("return -1;", ret.print());
+    }
+
+    @Test
+    public void testChapter2MulPeephole() {
+        Parser parser = new Parser("return 2*3;");
+        StopNode ret = parser.parse();
+        assertEquals("return 6;", ret.print());
+    }
+
+    @Test
+    public void testChapter2DivPeephole() {
+        Parser parser = new Parser("return 6/3;");
+        StopNode ret = parser.parse();
+        assertEquals("return 2;", ret.print());
+    }
+
+    @Test
+    public void testChapter2MinusPeephole() {
+        Parser parser = new Parser("return 6/-3;");
+        StopNode ret = parser.parse();
+        assertEquals("return -2;", ret.print());
+    }
+
+    @Test
+    public void testChapter2Example() {
+        Parser parser = new Parser("return 1+2*3+-5;");
+        StopNode ret = parser.parse();
+        assertEquals("return 2;", ret.print());
+        GraphVisualizer gv = new GraphVisualizer();
+        System.out.println(gv.generateDotOutput(parser));
+    }
+
+    @Test
+    public void testSimpleProgram() {
+        Parser parser = new Parser("return 1;");
+        StopNode stop = parser.parse();
+        StartNode start = Parser.START;
+        ReturnNode ret = (ReturnNode)stop.in(0);
+        
+        assertTrue(ret.ctrl() instanceof ProjNode);
+        Node expr = ret.expr();
+        if( expr instanceof ConstantNode con ) {
+            assertEquals(start,con.in(0));
+            assertEquals(TypeInteger.constant(1), con._type);
+        } else {
+            fail();
+        }
+    }
+
+    @Test
+    public void testZero() {
+        Parser parser = new Parser("return 0;");
+        parser.parse();
+        StartNode start = Parser.START;
+        for( Node use : start._outputs )
+            if( use instanceof ConstantNode con )
+                assertEquals(TypeInteger.constant(0),con._type);
+    }
+
+    @Test
+    public void testBad1() {
+        try { 
+            new Parser("ret").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, expected =: ",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testBad2() {
+        try { 
+            new Parser("return 0123;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error: integer values cannot start with '0'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testNotBad3() {
+        // this test used to fail in chapter 1
+        assertEquals("return 12;", new Parser("return --12;").parse().print());
+    }
+
+    @Test
+    public void testBad4() {
+        try { 
+            new Parser("return 100").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, expected ;: ",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testNotBad5() {
+        // this test used to fail in chapter 1
+        assertEquals("return -100;", new Parser("return -100;").parse().print());
+    }
+
+    @Test
+    public void testBad6() {
+        try {
+            new Parser("int a=1; int b=2; int c=0; { int b=3; c=a+b;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, expected }: ",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testBad7() {
+        try {
+            new Parser("return 1;}").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, unexpected }",e.getMessage());
+        }
+    }
+
+}