fix (parser): don't panic if assign of define untyped value (#10)

* fix (parser): don't panic if assign of define untyped value

In case of defining or assigning to untyped value, the type has
to be taken from the source value instead of the target value.

The vm test coverage has also been slightly improved.

* fix and simplify Token.Name()

* improve parser errors

1 files changed, 9 insertions, 7 deletions

diff --git a/parser/type.go b/parser/type.go
index ba60e8f..e25431a 100644
--- a/parser/type.go
+++ b/parser/type.go
@@ -20,10 +20,12 @@ const (
 
 // Type parsing error definitions.
 var (
-	ErrInvalidType        = errors.New("invalid type")
-	ErrMissingType        = errors.New("missing type")
-	ErrSyntax             = errors.New("syntax error")
-	ErrTypeNotImplemented = errors.New("not implemented")
+	ErrFuncType       = errors.New("invalid function type")
+	ErrInvalidType    = errors.New("invalid type")
+	ErrMissingType    = errors.New("missing type")
+	ErrSize           = errors.New("invalid size")
+	ErrSyntax         = errors.New("syntax error")
+	ErrNotImplemented = errors.New("not implemented")
 )
 
 func (p *Parser) parseTypeExpr(in Tokens) (typ *vm.Type, err error) {
@@ -44,7 +46,7 @@ func (p *Parser) parseTypeExpr(in Tokens) (typ *vm.Type, err error) {
 			}
 			size, ok := constValue(cval).(int)
 			if !ok {
-				return nil, fmt.Errorf("invalid size")
+				return nil, ErrSize
 			}
 			return vm.ArrayOf(size, typ), nil
 		}
@@ -71,7 +73,7 @@ func (p *Parser) parseTypeExpr(in Tokens) (typ *vm.Type, err error) {
 		case l >= 2 && in1.Tok == lang.ParenBlock:
 			indexArgs, out = 1, in[2:]
 		default:
-			return nil, fmt.Errorf("invalid func signature")
+			return nil, ErrFuncType
 		}
 
 		// We can now parse function input and output parameter types.
@@ -125,7 +127,7 @@ func (p *Parser) parseTypeExpr(in Tokens) (typ *vm.Type, err error) {
 		return vm.StructOf(fields), nil
 
 	default:
-		return nil, fmt.Errorf("%w: %v", ErrTypeNotImplemented, in[0].Name())
+		return nil, fmt.Errorf("%w: %v", ErrNotImplemented, in[0].Name())
 	}
 }