Add positional_count field to Lambda

This field is used for static optimization, determining if parameters
are purely positional.

src/ast/parser.rs

@@ -227,17 +227,22 @@ impl<'a> Parser<'a> {
 
         let mut elements = Vec::new();
         while *self.peek() != TokenKind::RightBracket {
-            let next_token = self.advance()?;
-            let p_identity = Rc::new(NodeIdentity { location: next_token.location });
-            match next_token.kind {
+            let next_peek = self.peek();
+            match next_peek {
                 TokenKind::Identifier(name) => {
+                    let name = name.clone();
+                    let token = self.advance()?;
+                    let p_identity = Rc::new(NodeIdentity { location: token.location });
                     elements.push(Node {
                         identity: p_identity,
                         kind: UntypedKind::Parameter(name.into()),
                         ty: (),
                     });
                 },
-                _ => return Err(format!("Expected identifier in param vector, found {:?}", next_token.kind)),
+                TokenKind::LeftBracket => {
+                    elements.push(self.parse_param_vector()?);
+                },
+                _ => return Err(format!("Expected identifier or nested parameter vector, found {:?}", next_peek)),
             }
         }
         self.expect(TokenKind::RightBracket)?;