From 0e6bf2b27eb20cc697133f5124ba75457c333b2e Mon Sep 17 00:00:00 2001
From: Alex Bethel <abethel@cs.nmt.edu>
Date: Mon, 14 Jun 2021 16:19:56 -0500
Subject: [PATCH] Use pass-by-reference for variables, pass-by-value for
 expressions

---
 src/ast.rs       |  6 +-----
 src/interpret.rs | 24 +++++++++++++++---------
 src/parser.rs    |  5 +----
 3 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/src/ast.rs b/src/ast.rs
index dcc1d2fa..835e679f 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -70,11 +70,7 @@ pub enum StmtKind {
     },
     Call {
         iden: Iden,
-
-        // NOTE(Alex): Function arguments are Iden's, not Expr's,
-        // because they're passed by reference rather than by value
-        // and therefore need to be assignable.
-        args: Vec<Iden>,
+        args: Vec<Expr>,
     },
     Print(Expr),
     Melo(Iden),
diff --git a/src/interpret.rs b/src/interpret.rs
index b81ac7c4..bb4aa85c 100644
--- a/src/interpret.rs
+++ b/src/interpret.rs
@@ -20,7 +20,7 @@ use std::{
 use rand::random;
 
 use crate::{
-    ast::{Expr, Iden, Stmt, StmtKind},
+    ast::{Expr, ExprKind, Iden, Stmt, StmtKind},
     base_55,
     error::{Error, ErrorKind},
     variables::{Functio, Value, Variable},
@@ -286,16 +286,22 @@ impl ExecEnv {
     /// Call a function with the given arguments (i.e., actual
     /// parameters). If the function invocation fails for some reason,
     /// report the error at `span`.
-    fn fn_call(
-        &mut self,
-        func: Functio,
-        args: &[Iden],
-        span: &Range<usize>,
-    ) -> Result<(), Error> {
+    fn fn_call(&mut self, func: Functio, args: &[Expr], span: &Range<usize>) -> Result<(), Error> {
+        // Arguments that are ExprKind::Variable are pass by
+        // reference; all other expressions are pass by value.
         let args = args
             .iter()
-            .map(|arg| self.get_var_rc(arg))
-            .collect::<Result<Vec<Rc<RefCell<Value>>>, Error>>()?;
+            .map(|arg| {
+                if let ExprKind::Variable(name) = &arg.kind {
+                    self.get_var_rc(&Iden {
+                        iden: name.to_owned(),
+                        span: arg.span.clone(),
+                    })
+                } else {
+                    self.eval_expr(arg).map(|v| Rc::new(RefCell::new(v)))
+                }
+            })
+            .collect::<Result<Vec<_>, Error>>()?;
 
         match func {
             Functio::BfFunctio {
diff --git a/src/parser.rs b/src/parser.rs
index 3d8797af..53b4cee4 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -469,10 +469,7 @@ impl<'source> Parser<'source> {
         }
 
         self.require(Token::Semicolon)?;
-        // Ok(StmtKind::Call { iden, args })
-
-        // `args` needs to be a vector of Idens now. ~~Alex
-        todo!()
+        Ok(StmtKind::Call { iden, args })
     }
 
     /// Parse variable declaration