refactor: use macro for arg counting

src/evaluator/env.rs

@@ -1,5 +1,6 @@
 use std::{borrow::Borrow, cell::RefCell, collections::HashMap, rc::Rc};
 
+use super::macros::arg_count;
 use super::{eval_ast_node, Error, Expression};
 use crate::parser::Node;
 
@@ -130,9 +131,7 @@ pub fn core_environment() -> Rc<Environment> {
         (
             "eq?",
             Expression::NativeFunc(|args| {
-                if args.len() != 2 {
+                arg_count!(2, args.len());
-                    Err(Error::MismatchedArgCount(2, args.len()))?
-                }
 
                 if args[0] == args[1] {
                     return Ok(Expression::Boolean(true).into());
@@ -144,9 +143,7 @@ pub fn core_environment() -> Rc<Environment> {
         (
             "not",
             Expression::NativeFunc(|args| {
-                if args.len() != 1 {
+                arg_count!(1, args.len());
-                    Err(Error::MismatchedArgCount(1, args.len()))?
-                }
 
                 if *args[0] == Expression::Boolean(false) {
                     return Ok(Expression::Boolean(true).into());
@@ -158,9 +155,7 @@ pub fn core_environment() -> Rc<Environment> {
         (
             "<",
             Expression::NativeFunc(|args| {
-                if args.len() != 2 {
+                arg_count!(2, args.len());
-                    Err(Error::MismatchedArgCount(2, args.len()))?
-                }
 
                 let less_than = match (args[0].borrow(), args[1].borrow()) {
                     (Expression::Int(lhs), Expression::Int(rhs)) => lhs < rhs,
@@ -173,9 +168,7 @@ pub fn core_environment() -> Rc<Environment> {
         (
             ">",
             Expression::NativeFunc(|args| {
-                if args.len() != 2 {
+                arg_count!(2, args.len());
-                    Err(Error::MismatchedArgCount(2, args.len()))?
-                }
 
                 let greater_than = match (args[0].borrow(), args[1].borrow()) {
                     (Expression::Int(lhs), Expression::Int(rhs)) => lhs > rhs,
@@ -188,9 +181,7 @@ pub fn core_environment() -> Rc<Environment> {
         (
             "<=",
             Expression::NativeFunc(|args| {
-                if args.len() != 2 {
+                arg_count!(2, args.len());
-                    Err(Error::MismatchedArgCount(2, args.len()))?
-                }
 
                 let less_than_equal = match (args[0].borrow(), args[1].borrow()) {
                     (Expression::Int(lhs), Expression::Int(rhs)) => lhs <= rhs,
@@ -203,9 +194,7 @@ pub fn core_environment() -> Rc<Environment> {
         (
             ">=",
             Expression::NativeFunc(|args| {
-                if args.len() != 2 {
+                arg_count!(2, args.len());
-                    Err(Error::MismatchedArgCount(2, args.len()))?
-                }
 
                 let greater_than_equal = match (args[0].borrow(), args[1].borrow()) {
                     (Expression::Int(lhs), Expression::Int(rhs)) => lhs >= rhs,
@@ -219,9 +208,7 @@ pub fn core_environment() -> Rc<Environment> {
         (
             "if",
             Expression::NativeFunc(|args| {
-                if args.len() != 3 {
+                arg_count!(3, args.len());
-                    Err(Error::MismatchedArgCount(3, args.len()))?
-                }
 
                 let (cond, consequence, alternative) =
                     (args[0].clone(), args[1].clone(), args[2].clone());
@@ -239,9 +226,7 @@ pub fn core_environment() -> Rc<Environment> {
             "define!",
             Expression::Special(|env, args| {
                 let mut args = args.into_iter();
-                if args.len() != 2 {
+                arg_count!(2, args.len());
-                    Err(Error::MismatchedArgCount(2, args.len()))?
-                }
 
                 let key = match args.next().unwrap() {
                     Node::Symbol(name) => name,
@@ -258,9 +243,7 @@ pub fn core_environment() -> Rc<Environment> {
         (
             "let*",
             Expression::Special(|env, args| {
-                if args.len() != 2 {
+                arg_count!(2, args.len());
-                    Err(Error::MismatchedArgCount(2, args.len()))?
-                }
 
                 let mut args = args.into_iter();
                 let new_env = match args.next().unwrap() {
@@ -288,9 +271,7 @@ pub fn core_environment() -> Rc<Environment> {
             "fn*",
             Expression::Special(|env, args| {
                 let mut args = args;
-                if args.len() != 2 {
+                arg_count!(2, args.len());
-                    Err(Error::MismatchedArgCount(2, args.len()))?
-                }
 
                 let arg_list = args.remove(0);
                 let body = args.remove(0);
@@ -317,9 +298,7 @@ pub fn core_environment() -> Rc<Environment> {
         (
             "display",
             Expression::NativeFunc(|args| {
-                if args.len() != 1 {
+                arg_count!(1, args.len());
-                    Err(Error::MismatchedArgCount(1, args.len()))?
-                }
 
                 print!("{}", args[0]);
 

src/evaluator/macros.rs

@@ -0,0 +1,10 @@
+#[macro_export]
+macro_rules! arg_count {
+    ($expected:expr, $given:expr) => {
+        if $expected != $given {
+            Err(Error::MismatchedArgCount($expected, $given))?
+        }
+    };
+}
+
+pub(crate) use arg_count;

src/evaluator/mod.rs

@@ -6,6 +6,8 @@ use thiserror::Error;
 use crate::parser::Node;
 
 mod env;
+mod macros;
+
 pub use env::{core_environment, Environment};
 
 #[derive(Debug, PartialEq)]