From 30ab0cf7daa0267821f0e1a2d08099e3e7c58f6c Mon Sep 17 00:00:00 2001
From: Erin <erin@erindesu.cz>
Date: Sat, 22 Jan 2022 20:37:44 +0100
Subject: [PATCH] Implemented Len in parser

---
 ablescript/src/ast.rs       |  1 +
 ablescript/src/interpret.rs |  1 +
 ablescript/src/parser.rs    | 26 ++++++++++++++++++++++----
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/ablescript/src/ast.rs b/ablescript/src/ast.rs
index a5f1905..3a7941e 100644
--- a/ablescript/src/ast.rs
+++ b/ablescript/src/ast.rs
@@ -190,6 +190,7 @@ pub enum ExprKind {
         expr: Box<Expr>,
         index: Box<Expr>,
     },
+    Len(Box<Expr>),
     Variable(String),
 }
 
diff --git a/ablescript/src/interpret.rs b/ablescript/src/interpret.rs
index 183eb9f..044e9e3 100644
--- a/ablescript/src/interpret.rs
+++ b/ablescript/src/interpret.rs
@@ -175,6 +175,7 @@ impl ExecEnv {
                     .map(|x| x.borrow().clone())
                     .unwrap_or(Value::Nul)
             }
+            Len(_) => todo!("length"),
 
             // TODO: not too happy with constructing an artificial
             // Ident here.
diff --git a/ablescript/src/parser.rs b/ablescript/src/parser.rs
index 6f7ebb6..9fd351e 100644
--- a/ablescript/src/parser.rs
+++ b/ablescript/src/parser.rs
@@ -195,10 +195,7 @@ impl<'source> Parser<'source> {
 
             Token::LeftBracket => match buf.take() {
                 Some(buf) => Ok(Expr::new(
-                    ExprKind::Index {
-                        expr: Box::new(buf),
-                        index: Box::new(self.expr_flow(Token::RightBracket)?),
-                    },
+                    self.index_flow(buf)?,
                     start..self.lexer.span().end,
                 )),
                 None => Ok(Expr::new(self.cart_flow()?, start..self.lexer.span().end)),
@@ -279,6 +276,27 @@ impl<'source> Parser<'source> {
         Ok(ExprKind::Cart(cart))
     }
 
+    /// Flow for indexing operations
+    ///
+    /// Indexing with empty index resolves to length of expression, else it indexes
+    fn index_flow(&mut self, expr: Expr) -> Result<ExprKind, Error> {
+        let mut buf = None;
+        Ok(loop {
+            match self.checked_next()? {
+                Token::RightBracket => match buf {
+                    Some(index) => {
+                        break ExprKind::Index {
+                            expr: Box::new(expr),
+                            index: Box::new(index),
+                        }
+                    }
+                    None => break ExprKind::Len(Box::new(expr)),
+                },
+                token => buf = Some(self.parse_expr(token, &mut buf)?),
+            }
+        })
+    }
+
     /// Flow for operators
     ///
     /// Generates operation from LHS buffer and next expression as RHS