implement broken first and rest functions

src/lib/environ.rs

@@ -87,8 +87,6 @@ pub fn default_env<'a>() -> Environ<'a> {
         }),
     );
 
-
-
     data.insert("=".to_string(), Expr::Func(ensure_tonicity!(|a, b| a == b)));
     data.insert(">".to_string(), Expr::Func(ensure_tonicity!(|a, b| a > b)));
     data.insert(

src/lib/evaluate.rs

@@ -14,7 +14,7 @@ pub fn eval(exp: &Expr, env: &mut Environ) -> Result<Expr, RispError> {
         Expr::Bool(_a) => Ok(exp.clone()),
         Expr::Number(_a) => Ok(exp.clone()),
 
-        Expr::Str(_a)=>{ Ok(exp.clone())} 
+        Expr::Str(_a) => Ok(exp.clone()),
 
         Expr::List(list) => {
             let first_form = list
@@ -40,6 +40,7 @@ pub fn eval(exp: &Expr, env: &mut Environ) -> Result<Expr, RispError> {
         }
         Expr::Func(_) => Err(RispError::Reason("unexpected form".to_string())),
         Expr::Lambda(_) => Err(RispError::Reason("unexpected form".to_string())),
+        // Expr::Nil => Err(RispError::Reason("unexpected nil".to_string())),
     }
 }
 
@@ -98,12 +99,48 @@ fn eval_built_in_form(
             "if" => Some(eval_if_args(arg_forms, env)),
             "def" => Some(eval_def_args(arg_forms, env)),
             "fn" => Some(eval_lambda_args(arg_forms)),
+            "first" => Some(eval_first_args(arg_forms, env)),
+            "rest" => Some(eval_rest_args(arg_forms)),
             _ => None,
         },
 
         _ => None,
     }
 }
+fn eval_first_args(arg_forms: &[Expr], env: &mut Environ) -> Result<Expr, RispError> {
+    if arg_forms.first().is_some() {
+        let first = arg_forms.first().unwrap();
+        let ret: Result<Expr, RispError> = match first {
+            Expr::List(vec) => Ok(vec.first().unwrap().clone()),
+            // Expr::Func(a) => a(),
+            Expr::Lambda(lambda) => eval(&Expr::Lambda(lambda.clone()), env),
+            _ => Ok(Expr::List(Vec::new())),
+        };
+        return Ok(ret.unwrap());
+    } else {
+        Ok(Expr::List(Vec::new()))
+    }
+}
+
+fn eval_rest_args(mut arg_forms: &[Expr]) -> Result<Expr, RispError> {
+    if arg_forms.first().is_some() {
+        // let first = arg_forms.first().unwrap();
+        let first = arg_forms.take_first().unwrap();
+        match first {
+            Expr::List(vec) => {
+                let mut rest_vec = vec.clone();
+                if rest_vec.len() == 0 {
+                    return Ok(Expr::List(Vec::new()));
+                }
+                let _first = rest_vec.remove(0);
+
+                return Ok(Expr::List(rest_vec.to_vec()));
+            }
+            _ => return Ok(Expr::List(Vec::new())),
+        }
+    }
+    Ok(Expr::List(Vec::new()))
+}
 
 fn eval_lambda_args(arg_forms: &[Expr]) -> Result<Expr, RispError> {
     let params_exp = arg_forms

src/lib/mod.rs

@@ -1,5 +1,5 @@
-use std::fmt;
 use core::num::ParseFloatError;
+use std::fmt;
 
 pub use std::collections::HashMap;
 pub use std::io::Write;
@@ -7,8 +7,8 @@ pub use std::rc::Rc;
 
 mod environ;
 pub use environ::default_env;
-pub use environ::Environ;
 pub use environ::env_get;
+pub use environ::Environ;
 
 mod parser;
 pub use parser::parse;

src/main.rs

@@ -1,3 +1,4 @@
+#![feature(slice_take)]
 #![allow(special_module_name)]
 use std::io;
 use std::io::Write;
@@ -15,9 +16,8 @@ fn slurp_expr() -> String {
     expr
 }
 
-
 fn extend_environ<'a>(mut env: Environ<'a>) -> Environ<'a> {
-     env.data.insert(
+    env.data.insert(
         "quit".to_string(),
         Expr::Func(|_args: &[Expr]| -> Result<Expr, RispError> {
             // TODO: let this function take in arguments
@@ -28,11 +28,8 @@ fn extend_environ<'a>(mut env: Environ<'a>) -> Environ<'a> {
         }),
     );
 
-   env.data.insert(
-        "prompt".to_string(),
-        Expr::Symbol("rlisp => ".to_string()),
-    );
-
+    env.data
+        .insert("prompt".to_string(), Expr::Symbol("rlisp => ".to_string()));
 
     env.data.insert(
         "print".to_string(),
@@ -50,8 +47,6 @@ fn extend_environ<'a>(mut env: Environ<'a>) -> Environ<'a> {
     env
 }
 
-
-
 fn main() {
     let env = &mut default_env();
     let env = &mut extend_environ(env.clone());