Make world.Define{Const,Var} indicate if the definition was

successful.

R=rsc
APPROVED=rsc
DELTA=43  (31 added, 0 deleted, 12 changed)
OCL=34375
CL=34397

usr/austin/eval/scope.go

@@ -142,13 +142,13 @@ func (b *block) defineSlot(t Type, temp bool) *Variable {
 	return v;
 }
 
-func (b *block) DefineConst(name string, pos token.Position, t Type, v Value) *Constant {
-	if _, ok := b.defs[name]; ok {
-		return nil;
+func (b *block) DefineConst(name string, pos token.Position, t Type, v Value) (*Constant, Def) {
+	if prev, ok := b.defs[name]; ok {
+		return nil, prev;
 	}
 	c := &Constant{pos, t, v};
 	b.defs[name] = c;
-	return c;
+	return c, nil;
 }
 
 func (b *block) DefineType(name string, pos token.Position, t Type) Type {

usr/austin/eval/stmt.go

@@ -365,7 +365,7 @@ func (a *stmtCompiler) compileVarDecl(decl *ast.GenDecl) {
 				a.defineVar(n, t);
 			}
 		} else {
-			// Decalaration with assignment
+			// Declaration with assignment
 			lhs := make([]ast.Expr, len(spec.Names));
 			for i, n := range spec.Names {
 				lhs[i] = n;
@@ -388,9 +388,17 @@ func (a *stmtCompiler) compileDecl(decl ast.Decl) {
 		}
 		// Declare and initialize v before compiling func
 		// so that body can refer to itself.
-		c := a.block.DefineConst(d.Name.Value, a.pos, decl.Type, decl.Type.Zero());
+		c, prev := a.block.DefineConst(d.Name.Value, a.pos, decl.Type, decl.Type.Zero());
+		if prev != nil {
+			pos := prev.Pos();
+			if pos.IsValid() {
+				a.diagAt(d.Name, "identifier %s redeclared in this block\n\tprevious declaration at %s", d.Name.Value, &pos);
+			} else {
+				a.diagAt(d.Name, "identifier %s redeclared in this block", d.Name.Value);
+			}
+		}
 		fn := a.compileFunc(a.block, decl, d.Body);
-		if fn == nil {
+		if c == nil || fn == nil {
 			return;
 		}
 		var zeroThread Thread;

usr/austin/eval/world.go

@@ -5,6 +5,7 @@
 package eval
 
 import (
+	"fmt";
 	"go/ast";
 	"go/parser";
 	"go/scanner";
@@ -154,12 +155,34 @@ func (w *World) Compile(text string) (Code, os.Error) {
 	return nil, err;
 }
 
-func (w *World) DefineConst(name string, t Type, val Value) {
-	w.scope.DefineConst(name, token.Position{}, t, val);
+type RedefinitionError struct {
+	Name string;
+	Prev Def;
 }
 
-func (w *World) DefineVar(name string, t Type, val Value) {
-	v, _ := w.scope.DefineVar(name, token.Position{}, t);
+func (e *RedefinitionError) String() string {
+	res := "identifier " + e.Name + " redeclared";
+	pos := e.Prev.Pos();
+	if pos.IsValid() {
+		res += "; previous declaration at " + pos.String();
+	}
+	return res;
+}
+
+func (w *World) DefineConst(name string, t Type, val Value) os.Error {
+	_, prev := w.scope.DefineConst(name, token.Position{}, t, val);
+	if prev != nil {
+		return &RedefinitionError{name, prev};
+	}
+	return nil;
+}
+
+func (w *World) DefineVar(name string, t Type, val Value) os.Error {
+	v, prev := w.scope.DefineVar(name, token.Position{}, t);
+	if prev != nil {
+		return &RedefinitionError{name, prev};
+	}
 	v.Init = val;
+	return nil;
 }