From f94f22a3d0aeff98cc9169c94b683aa139e9c81c Mon Sep 17 00:00:00 2001
From: Akshay <nerdy@peppe.rs>
Date: Sat, 27 Mar 2021 13:16:25 +0530
Subject: implement char literals

---
 src/lisp/eval.rs | 53 ++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 38 insertions(+), 15 deletions(-)

(limited to 'src/lisp/eval.rs')

diff --git a/src/lisp/eval.rs b/src/lisp/eval.rs
index 5accec4..370b624 100644
--- a/src/lisp/eval.rs
+++ b/src/lisp/eval.rs
@@ -2,7 +2,7 @@ use crate::{
     app::AppState,
     lisp::{
         error::{EvalError, LispError},
-        expr::{Ident, LispExpr, LispFunction},
+        expr::{Arity, Ident, LispExpr, LispFunction},
         number::LispNumber,
         EnvList, Environment,
     },
@@ -16,6 +16,7 @@ pub fn eval(expr: &LispExpr, app: &mut AppState) -> Result<LispExpr, LispError>
     match expr {
         LispExpr::Unit => Ok(expr.clone()),
         LispExpr::StringLit(_) => Ok(expr.clone()),
+        LispExpr::Char(_) => Ok(expr.clone()),
         LispExpr::Number(_) => Ok(expr.clone()),
         LispExpr::BoolLit(_) => Ok(expr.clone()),
         LispExpr::Ident(ref id) => lookup_extended(&app.lisp_env, id),
@@ -26,6 +27,7 @@ pub fn eval(expr: &LispExpr, app: &mut AppState) -> Result<LispExpr, LispError>
                     "define" => define_var(&li[1..], app),
                     "set!" => set_var(&li[1..], app),
                     "lambda" => create_lambda(&li[1..]),
+                    "if" => eval_if(&li[1..], app),
                     _ => {
                         let func_expr = eval(&func_expr, app)?;
                         match func_expr {
@@ -37,17 +39,17 @@ pub fn eval(expr: &LispExpr, app: &mut AppState) -> Result<LispExpr, LispError>
                                 f.call(&args, app)
                             }
                             LispExpr::Function(f) => {
-                                info!("eval custom func");
                                 let mut args = Vec::new();
                                 for item in li[1..].iter() {
-                                    args.push(eval(item, app)?);
+                                    let i = eval(item, app)?;
+                                    args.push(i);
                                 }
                                 if f.params.len() != args.len() {
                                     info!("too many or too little number of args");
-                                    Err(EvalError::ArgumentCount(Some(f.params.len() as u32))
+                                    Err(EvalError::ArgumentCount(Arity::Exact(f.params.len()))
                                         .into())
                                 } else {
-                                    let mut nested_env: Environment =
+                                    let nested_env: Environment =
                                         f.params.into_iter().zip(args).collect();
                                     app.lisp_env.push(nested_env);
                                     let result = if f.body.is_empty() {
@@ -71,9 +73,9 @@ pub fn eval(expr: &LispExpr, app: &mut AppState) -> Result<LispExpr, LispError>
 }
 
 pub fn define_var(args: &[LispExpr], app: &mut AppState) -> Result<LispExpr, LispError> {
-    if args.len() != 2 {
-        error!("Invalid arity for `define`");
-        return Err(EvalError::ArgumentCount(Some(2)).into());
+    let arity = Arity::Exact(2);
+    if !arity.is_valid(args) {
+        return Err(arity.to_error());
     }
     match args {
         [LispExpr::Ident(id), expr] => {
@@ -107,6 +109,7 @@ pub fn define_var(args: &[LispExpr], app: &mut AppState) -> Result<LispExpr, Lis
 
             let local_env = app.lisp_env.last_mut();
             if let Some(env) = local_env {
+                info!("creating function {}", id);
                 env.insert(id.into(), value);
             } else {
                 error!("Unable to create global definition");
@@ -122,9 +125,9 @@ pub fn define_var(args: &[LispExpr], app: &mut AppState) -> Result<LispExpr, Lis
 }
 
 pub fn set_var(args: &[LispExpr], app: &mut AppState) -> Result<LispExpr, LispError> {
-    if args.len() != 2 {
-        error!("Invalid arity for `define`");
-        return Err(EvalError::ArgumentCount(Some(2)).into());
+    let arity = Arity::Exact(2);
+    if !arity.is_valid(args) {
+        return Err(arity.to_error());
     }
     match args {
         [LispExpr::Ident(id), expr] => {
@@ -147,10 +150,9 @@ pub fn set_var(args: &[LispExpr], app: &mut AppState) -> Result<LispExpr, LispEr
 }
 
 pub fn create_lambda(cdr: &[LispExpr]) -> Result<LispExpr, LispError> {
-    if cdr.len() != 2 {
-        // needs params and body
-        error!("needs params and body");
-        return Err(EvalError::ArgumentCount(Some(2)).into());
+    let arity: Arity = Arity::Exact(2);
+    if !arity.is_valid(cdr) {
+        return Err(arity.to_error());
     }
     info!("creating lambda");
     match cdr {
@@ -172,6 +174,27 @@ pub fn create_lambda(cdr: &[LispExpr]) -> Result<LispExpr, LispError> {
     }
 }
 
+pub fn eval_if(args: &[LispExpr], app: &mut AppState) -> Result<LispExpr, LispError> {
+    let arity = Arity::Exact(3);
+    if !arity.is_valid(args) {
+        return Err(arity.to_error());
+    } else {
+        match args {
+            [predicate, then, else_] => {
+                let predicate = eval(&predicate, app)?;
+                if matches!(predicate, LispExpr::BoolLit(false)) {
+                    return eval(&else_, app);
+                } else {
+                    return eval(&then, app);
+                }
+            }
+            _ => {
+                panic!("panicked at `if` expression")
+            }
+        }
+    }
+}
+
 pub fn lookup_extended(env_list: &[Environment], key: &str) -> Result<LispExpr, LispError> {
     if env_list.is_empty() {
         return Err(EvalError::UnboundVariable(key.into()).into());
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