Simplified block parsing

src/build/ast/Parse.go

@@ -27,12 +27,14 @@ func Parse(tokens token.List) (AST, error) {
 // toASTNode generates an AST node from an instruction.
 func toASTNode(tokens token.List) (Node, error) {
 	if tokens[0].Kind == token.Keyword {
-		switch tokens[0].Text() {
-		case keyword.Return:
+		word := tokens[0].Text()
+
+		if word == keyword.Return {
 			value := expression.Parse(tokens[1:])
 			return &Return{Value: value}, nil
+		}
 
-		case keyword.Loop:
+		if keywordHasBlock(word) {
 			blockStart := tokens.IndexKind(token.BlockStart)
 			blockEnd := tokens.LastIndexKind(token.BlockEnd)
 
@@ -45,29 +47,20 @@ func toASTNode(tokens token.List) (Node, error) {
 			}
 
 			body, err := Parse(tokens[blockStart+1 : blockEnd])
-			return &Loop{Body: body}, err
 
+			switch word {
 			case keyword.If:
-			blockStart := tokens.IndexKind(token.BlockStart)
-			blockEnd := tokens.LastIndexKind(token.BlockEnd)
-
-			if blockStart == -1 {
-				return nil, errors.New(errors.MissingBlockStart, nil, tokens[0].End())
-			}
-
-			if blockEnd == -1 {
-				return nil, errors.New(errors.MissingBlockEnd, nil, tokens[len(tokens)-1].End())
-			}
-
 				condition := expression.Parse(tokens[1:blockStart])
-			body, err := Parse(tokens[blockStart+1 : blockEnd])
 				return &If{Condition: condition, Body: body}, err
 
-		default:
-			return nil, errors.New(&errors.KeywordNotImplemented{Keyword: tokens[0].Text()}, nil, tokens[0].Position)
+			case keyword.Loop:
+				return &Loop{Body: body}, err
 			}
 		}
 
+		return nil, errors.New(&errors.KeywordNotImplemented{Keyword: word}, nil, tokens[0].Position)
+	}
+
 	expr := expression.Parse(tokens)
 
 	if expr == nil {
@@ -115,3 +108,8 @@ func IsFunctionCall(expr *expression.Expression) bool {
 func IsVariableDefinition(expr *expression.Expression) bool {
 	return expr.Token.Kind == token.Operator && expr.Token.Text() == ":="
 }
+
+// keywordHasBlock returns true if the keyword requires a block.
+func keywordHasBlock(word string) bool {
+	return word == keyword.If || word == keyword.Loop
+}