From 288e2f4feb04197301adac2673c1b0031acb25ea Mon Sep 17 00:00:00 2001
From: Roman Godmaire <godmaire@twilit.io>
Date: Sat, 17 Feb 2024 06:58:22 -0500
Subject: [PATCH] fix: provide details on argument count errors

---
 src/evaluator/env.rs | 12 ++++++------
 src/evaluator/mod.rs |  6 +++---
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/src/evaluator/env.rs b/src/evaluator/env.rs
index e5139ba..685acb9 100644
--- a/src/evaluator/env.rs
+++ b/src/evaluator/env.rs
@@ -107,7 +107,7 @@ pub fn core_environment() -> Rc<Environment> {
             "hashmap",
             Expression::NativeFunc(|args| {
                 if args.len() % 2 != 0 {
-                    Err(Error::MismatchedArgCount)?
+                    Err(Error::MismatchedArgCount(2, args.len()))?
                 }
 
                 let mut index = -1;
@@ -132,7 +132,7 @@ pub fn core_environment() -> Rc<Environment> {
             "if",
             Expression::NativeFunc(|args| {
                 if args.len() != 3 {
-                    Err(Error::MismatchedArgCount)?
+                    Err(Error::MismatchedArgCount(3, args.len()))?
                 }
 
                 let (cond, consequence, alternative) =
@@ -152,7 +152,7 @@ pub fn core_environment() -> Rc<Environment> {
             Expression::Special(|env, args| {
                 let mut args = args.into_iter();
                 if args.len() != 2 {
-                    Err(Error::MismatchedArgCount)?
+                    Err(Error::MismatchedArgCount(2, args.len()))?
                 }
 
                 let key = match args.next().unwrap() {
@@ -171,7 +171,7 @@ pub fn core_environment() -> Rc<Environment> {
             "let*",
             Expression::Special(|env, args| {
                 if args.len() != 2 {
-                    Err(Error::MismatchedArgCount)?
+                    Err(Error::MismatchedArgCount(2, args.len()))?
                 }
 
                 let mut args = args.into_iter();
@@ -189,7 +189,7 @@ pub fn core_environment() -> Rc<Environment> {
                             outer: Some(env.clone()),
                         }
                     }
-                    Node::List(_) => Err(Error::MismatchedArgCount)?,
+                    Node::List(list) => Err(Error::MismatchedArgCount(2, list.len()))?,
                     _ => Err(Error::ExpectedList)?,
                 };
 
@@ -201,7 +201,7 @@ pub fn core_environment() -> Rc<Environment> {
             Expression::Special(|env, args| {
                 let mut args = args;
                 if args.len() != 2 {
-                    Err(Error::MismatchedArgCount)?
+                    Err(Error::MismatchedArgCount(2, args.len()))?
                 }
 
                 let arg_list = args.remove(0);
diff --git a/src/evaluator/mod.rs b/src/evaluator/mod.rs
index ecd9421..0e2ff06 100644
--- a/src/evaluator/mod.rs
+++ b/src/evaluator/mod.rs
@@ -89,8 +89,8 @@ pub enum Error {
     ExpectedSymbol,
     #[error("expected list")]
     ExpectedList,
-    #[error("incorrect number of arguments passed to function")]
-    MismatchedArgCount,
+    #[error("expected {0} arguments, got {1}")]
+    MismatchedArgCount(usize, usize),
 }
 
 pub fn eval(env: Rc<Environment>, ast: Vec<Node>) -> Result<Vec<Rc<Expression>>> {
@@ -137,7 +137,7 @@ fn eval_ast_node(env: Rc<Environment>, ast_node: Node) -> Result<Rc<Expression>>
                 } => {
                     let args = list;
                     if args.len() != params.len() {
-                        Err(Error::MismatchedArgCount)?
+                        Err(Error::MismatchedArgCount(params.len(), args.len()))?
                     }
 
                     let args = args