Implemented loop iterators

src/ast/Loop.go

@@ -1,6 +1,9 @@
 package ast
 
+import "git.akyoto.dev/cli/q/src/expression"
+
 // Loop represents a block of repeatable statements.
 type Loop struct {
+	Head *expression.Expression
 	Body AST
 }

src/ast/parseKeyword.go

@@ -40,8 +40,15 @@ func parseKeyword(tokens token.List, source []byte, nodes AST) (Node, error) {
 		return nil, err
 
 	case token.Loop:
-		_, _, body, err := block(tokens, source)
-		return &Loop{Body: body}, err
+		blockStart, _, body, err := block(tokens, source)
+		head := tokens[1:blockStart]
+
+		loop := &Loop{
+			Head: expression.Parse(head),
+			Body: body,
+		}
+
+		return loop, err
 
 	case token.Return:
 		if len(tokens) == 1 {