Simplified block parsing

src/build/ast/Parse.go

@@ -27,45 +27,38 @@ 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() {
+		word := tokens[0].Text()
-		case keyword.Return:
+
+		if word == keyword.Return {
 			value := expression.Parse(tokens[1:])
 			return &Return{Value: value}, nil
-
-		case keyword.Loop:
-			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())
-			}
-
-			body, err := Parse(tokens[blockStart+1 : blockEnd])
-			return &Loop{Body: body}, err
-
-		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)
 		}
+
+		if keywordHasBlock(word) {
+			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())
+			}
+
+			body, err := Parse(tokens[blockStart+1 : blockEnd])
+
+			switch word {
+			case keyword.If:
+				condition := expression.Parse(tokens[1:blockStart])
+				return &If{Condition: condition, Body: body}, err
+
+			case keyword.Loop:
+				return &Loop{Body: body}, err
+			}
+		}
+
+		return nil, errors.New(&errors.KeywordNotImplemented{Keyword: word}, nil, tokens[0].Position)
 	}
 
 	expr := expression.Parse(tokens)
@@ -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
+}