Implemented key extraction

ablescript/src/ast.rs

@@ -160,6 +160,7 @@ pub enum Expr {
         index: Box<Spanned<Expr>>,
     },
     Len(Box<Spanned<Expr>>),
+    Keys(Box<Spanned<Expr>>),
     Variable(String),
 }
 

ablescript/src/interpret.rs

@@ -195,7 +195,14 @@ impl ExecEnv {
                     .unwrap_or(Value::Nul)
             }
             Len(expr) => Value::Int(self.eval_expr(expr)?.length()),
-
+            Keys(expr) => Value::Cart(
+                self.eval_expr(expr)?
+                    .into_cart()
+                    .into_keys()
+                    .enumerate()
+                    .map(|(i, k)| (Value::Int(i as isize + 1), ValueRef::new(k)))
+                    .collect(),
+            ),
             // TODO: not too happy with constructing an artificial
             // Ident here.
             Variable(name) => {

ablescript/src/parser.rs

@@ -294,6 +294,10 @@ impl<'source> Parser<'source> {
                     }
                     None => break Expr::Len(Box::new(expr)),
                 },
+                Token::GreaterThan if buf.is_none() => {
+                    self.require(Token::RightBracket)?;
+                    break Expr::Keys(Box::new(expr));
+                }
                 token => buf = Some(self.parse_expr(token, &mut buf)?),
             }
         })