fix: catch mismatched types in binary operator expressions (#109)

The types of operands are checked prior to generate closures.

- test: improve evalCheck() to check against expected output and/or expected errors.

interp/cfg.go

@@ -428,6 +428,9 @@ func (interp *Interpreter) Cfg(root *Node) ([]*Node, error) {
 			wireChild(n)
 			n.findex = scope.inc(interp)
 			nilSym := interp.universe.sym["nil"]
+			if t0, t1 := n.child[0].typ, n.child[1].typ; !t0.untyped && !t1.untyped && t0.id() != t1.id() {
+				err = n.cfgError("mismatched types %s and %s", t0.id(), t1.id())
+			}
 			switch n.action {
 			case NotEqual:
 				n.typ = scope.getType("bool")

interp/interp.go

@@ -163,7 +163,7 @@ func initUniverse() *Scope {
 		"iota":  &Symbol{kind: Const, typ: &Type{cat: IntT}},
 
 		// predefined Go zero value
-		"nil": &Symbol{typ: &Type{cat: NilT}},
+		"nil": &Symbol{typ: &Type{cat: NilT, untyped: true}},
 
 		// predefined Go builtins
 		"append":  &Symbol{kind: Bltn, builtin: _append},

interp/interp_eval_test.go

@@ -209,6 +209,18 @@ func Foo() {
 	}
 }
 
+func TestEvalComparison(t *testing.T) {
+	i := interp.New(interp.Opt{})
+	evalCheck(t, i, `
+type Foo string
+type Bar string
+
+var a = Foo("test")
+var b = Bar("test")
+var c = a == b
+`, "", "7:9: mismatched types _.Foo and _.Bar")
+}
+
 func TestEvalCompositeArray0(t *testing.T) {
 	i := interp.New(interp.Opt{})
 	v := evalCheck(t, i, `a := []int{1, 2, 7: 20, 30}`)
@@ -226,12 +238,27 @@ func TestEvalUnary0(t *testing.T) {
 	}
 }
 
-func evalCheck(t *testing.T, i *interp.Interpreter, src string) reflect.Value {
+func evalCheck(t *testing.T, i *interp.Interpreter, src string, expect ...string) reflect.Value {
 	t.Helper()
 
 	res, err := i.Eval(src)
-	if err != nil {
-		t.Fatal(err)
+	if len(expect) == 0 {
+		if err != nil {
+			t.Fatal(err)
+		}
+		return res
+	}
+	if expect[0] != "" && expect[0] != fmt.Sprintf("%v", res) {
+		t.Fatalf("expected %v, got %v", expect[0], res)
+	}
+	if len(expect) == 1 {
+		if err != nil {
+			t.Fatal(err)
+		}
+		return res
+	}
+	if expect[1] != err.Error() {
+		t.Fatalf("expected error %v, got %v", expect[1], err.Error())
 	}
 	return res
 }

interp/type.go

@@ -386,9 +386,9 @@ func (t *Type) id() string {
 
 	res := ""
 	if t.cat == ValueT {
-		res = t.rtype.PkgPath() + t.rtype.Name()
+		res = t.rtype.PkgPath() + "." + t.rtype.Name()
 	} else {
-		res = t.pkgPath + t.name
+		res = t.pkgPath + "." + t.name
 	}
 	return res
 }