Implemented if statements

src/build/ast/AST.go

@@ -37,6 +37,15 @@ func (node *Define) String() string {
 	return fmt.Sprintf("(= %s %s)", node.Name.Text(), node.Value)
 }
 
+type If struct {
+	Condition *expression.Expression
+	Body      AST
+}
+
+func (node *If) String() string {
+	return fmt.Sprintf("(if %s %s)", node.Condition, node.Body)
+}
+
 type Loop struct {
 	Body AST
 }

src/build/ast/Parse.go

@@ -47,6 +47,22 @@ func toASTNode(tokens token.List) (Node, error) {
 			tree, err := Parse(tokens[blockStart:blockEnd])
 			return &Loop{Body: tree}, err
 
+		case keyword.If:
+			blockStart := tokens.IndexKind(token.BlockStart) + 1
+			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:token.BlockStart])
+			tree, err := Parse(tokens[blockStart:blockEnd])
+			return &If{Condition: condition, Body: tree}, err
+
 		default:
 			return nil, errors.New(&errors.KeywordNotImplemented{Keyword: tokens[0].Text()}, nil, tokens[0].Position)
 		}