small but full lisp

src/environ.rs

@@ -1,38 +1,78 @@
-use crate::Expr;
-use crate::RispError;
-use crate::HashMap;
 use crate::parse_list_of_floats;
+use crate::Expr;
+use crate::HashMap;
+use crate::RispError;
 
-pub 
-struct Environ {
-   pub data: HashMap<String, Expr>,
+macro_rules! ensure_tonicity {
+    ($check_fn:expr) => {{
+        |args: &[Expr]| -> Result<Expr, RispError> {
+            let floats = parse_list_of_floats(args)?;
+            let first = floats.first().ok_or(RispError::Reason(
+                "expected at least one number".to_string(),
+            ))?;
+            let rest = &floats[1..];
+            fn f(prev: &f64, xs: &[f64]) -> bool {
+                match xs.first() {
+                    Some(x) => $check_fn(prev, x) && f(x, &xs[1..]),
+                    None => true,
+                }
+            };
+            Ok(Expr::Bool(f(first, rest)))
+        }
+    }};
+}
+pub fn env_get(k: &str, env: &Environ) -> Option<Expr> {
+    match env.data.get(k) {
+        Some(exp) => Some(exp.clone()),
+        None => match &env.outer {
+            Some(outer_env) => env_get(k, &outer_env),
+            None => None,
+        },
+    }
 }
 
+#[derive(Clone)]
+pub struct Environ<'a> {
+    pub data: HashMap<String, Expr>,
+    pub outer: Option<&'a Environ<'a>>,
+}
 
-pub fn default_env() -> Environ {
+pub fn default_env<'a>() -> Environ<'a> {
     let mut data: HashMap<String, Expr> = HashMap::new();
     data.insert(
         "+".to_string(),
-    Expr::Func(
-      |args: &[Expr]| -> Result<Expr, RispError> {
-        let sum = parse_list_of_floats(args)?.iter().fold(0.0, |sum, a| sum + a);
+        Expr::Func(|args: &[Expr]| -> Result<Expr, RispError> {
+            let sum = parse_list_of_floats(args)?
+                .iter()
+                .fold(0.0, |sum, a| sum + a);
 
             Ok(Expr::Number(sum))
-      }
-    )
+        }),
     );
     data.insert(
         "-".to_string(),
-    Expr::Func(
-      |args: &[Expr]| -> Result<Expr, RispError> {
+        Expr::Func(|args: &[Expr]| -> Result<Expr, RispError> {
             let floats = parse_list_of_floats(args)?;
-        let first = *floats.first().ok_or(RispError::Reason("expected at least one number".to_string()))?;
+            let first = *floats.first().ok_or(RispError::Reason(
+                "expected at least one number".to_string(),
+            ))?;
             let sum_of_rest = floats[1..].iter().fold(0.0, |sum, a| sum + a);
 
             Ok(Expr::Number(first - sum_of_rest))
-      }
-    )
+        }),
     );
 
-  Environ {data}
+    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(
+        ">=".to_string(),
+        Expr::Func(ensure_tonicity!(|a, b| a >= b)),
+    );
+    data.insert("<".to_string(), Expr::Func(ensure_tonicity!(|a, b| a < b)));
+    data.insert(
+        "<=".to_string(),
+        Expr::Func(ensure_tonicity!(|a, b| a <= b)),
+    );
+
+    Environ { data, outer: None }
 }

src/evaluate.rs

@@ -0,0 +1,169 @@
+use crate::environ::env_get;
+use crate::Environ;
+use crate::Expr;
+use crate::HashMap;
+use crate::RLambda;
+use crate::Rc;
+use crate::RispError;
+
+pub fn eval(exp: &Expr, env: &mut Environ) -> Result<Expr, RispError> {
+    match exp {
+        Expr::Symbol(k) => {
+            env_get(k, env).ok_or(RispError::Reason(format!("unexpected symbol k='{}'", k)))
+        }
+        Expr::Bool(_a) => Ok(exp.clone()),
+        Expr::Number(_a) => Ok(exp.clone()),
+
+        Expr::List(list) => {
+            let first_form = list
+                .first()
+                .ok_or(RispError::Reason("expected a non-empty list".to_string()))?;
+            let arg_forms = &list[1..];
+            match eval_built_in_form(first_form, arg_forms, env) {
+                Some(res) => res,
+                None => {
+                    let first_eval = eval(first_form, env)?;
+                    match first_eval {
+                        Expr::Func(f) => f(&eval_forms(arg_forms, env)?),
+                        Expr::Lambda(lambda) => {
+                            let new_env = &mut env_for_lambda(lambda.params_exp, arg_forms, env)?;
+                            eval(&lambda.body_exp, new_env)
+                        }
+                        _ => Err(RispError::Reason(
+                            "first form must be a function".to_string(),
+                        )),
+                    }
+                }
+            }
+        }
+        Expr::Func(_) => Err(RispError::Reason("unexpected form".to_string())),
+        Expr::Lambda(_) => Err(RispError::Reason("unexpected form".to_string())),
+    }
+}
+
+fn eval_forms(arg_forms: &[Expr], env: &mut Environ) -> Result<Vec<Expr>, RispError> {
+    arg_forms.iter().map(|x| eval(x, env)).collect()
+}
+
+fn env_for_lambda<'a>(
+    params: Rc<Expr>,
+    arg_forms: &[Expr],
+    outer_env: &'a mut Environ,
+) -> Result<Environ<'a>, RispError> {
+    let ks = parse_list_of_symbol_strings(params)?;
+    if ks.len() != arg_forms.len() {
+        return Err(RispError::Reason(format!(
+            "expected {} arguments, got {}",
+            ks.len(),
+            arg_forms.len()
+        )));
+    }
+    let vs = eval_forms(arg_forms, outer_env)?;
+    let mut data: HashMap<String, Expr> = HashMap::new();
+    for (k, v) in ks.iter().zip(vs.iter()) {
+        data.insert(k.clone(), v.clone());
+    }
+    Ok(Environ {
+        data,
+        outer: Some(outer_env),
+    })
+}
+
+fn parse_list_of_symbol_strings(form: Rc<Expr>) -> Result<Vec<String>, RispError> {
+    let list = match form.as_ref() {
+        Expr::List(s) => Ok(s.clone()),
+        _ => Err(RispError::Reason(
+            "expected args form to be a list".to_string(),
+        )),
+    }?;
+    list.iter()
+        .map(|x| match x {
+            Expr::Symbol(s) => Ok(s.clone()),
+            _ => Err(RispError::Reason(
+                "expected symbols in the argument list".to_string(),
+            )),
+        })
+        .collect()
+}
+
+fn eval_built_in_form(
+    exp: &Expr,
+    arg_forms: &[Expr],
+    env: &mut Environ,
+) -> Option<Result<Expr, RispError>> {
+    match exp {
+        Expr::Symbol(s) => match s.as_ref() {
+            "if" => Some(eval_if_args(arg_forms, env)),
+            "def" => Some(eval_def_args(arg_forms, env)),
+            "fn" => Some(eval_lambda_args(arg_forms)),
+            _ => None,
+        },
+
+        _ => None,
+    }
+}
+
+fn eval_lambda_args(arg_forms: &[Expr]) -> Result<Expr, RispError> {
+    let params_exp = arg_forms
+        .first()
+        .ok_or(RispError::Reason("expected args form".to_string()))?;
+    let body_exp = arg_forms
+        .get(1)
+        .ok_or(RispError::Reason("expected second form".to_string()))?;
+    if arg_forms.len() > 2 {
+        return Err(RispError::Reason(
+            "fn definition can only have two forms ".to_string(),
+        ));
+    }
+
+    Ok(Expr::Lambda(RLambda {
+        body_exp: Rc::new(body_exp.clone()),
+        params_exp: Rc::new(params_exp.clone()),
+    }))
+}
+
+fn eval_if_args(arg_forms: &[Expr], env: &mut Environ) -> Result<Expr, RispError> {
+    let test_form = arg_forms
+        .first()
+        .ok_or(RispError::Reason("expected test form".to_string()))?;
+    let test_eval = eval(test_form, env)?;
+    match test_eval {
+        Expr::Bool(b) => {
+            let form_idx = if b { 1 } else { 2 };
+            let res_form = arg_forms
+                .get(form_idx)
+                .ok_or(RispError::Reason(format!("expected form idx={}", form_idx)))?;
+            let res_eval = eval(res_form, env);
+
+            res_eval
+        }
+        _ => Err(RispError::Reason(format!(
+            "unexpected test form='{}'",
+            test_form.to_string()
+        ))),
+    }
+}
+
+fn eval_def_args(arg_forms: &[Expr], env: &mut Environ) -> Result<Expr, RispError> {
+    let first_form = arg_forms
+        .first()
+        .ok_or(RispError::Reason("expected first form".to_string()))?;
+    let first_str = match first_form {
+        Expr::Symbol(s) => Ok(s.clone()),
+        _ => Err(RispError::Reason(
+            "expected first form to be a symbol".to_string(),
+        )),
+    }?;
+    let second_form = arg_forms
+        .get(1)
+        .ok_or(RispError::Reason("expected second form".to_string()))?;
+    if arg_forms.len() > 2 {
+        return Err(RispError::Reason(
+            "def can only have two forms ".to_string(),
+        ));
+    }
+    let second_eval = eval(second_form, env)?;
+    env.data.insert(first_str, second_eval);
+
+    Ok(first_form.clone())
+}

src/main.rs

@@ -1,103 +1,70 @@
-use std::io;
+use std::collections::HashMap;
 use std::fmt;
+use std::io;
+use std::io::Write;
 use std::num::ParseFloatError;
-use std::collections::HashMap;use std::io::Write;
+use std::rc::Rc;
 
 mod environ;
-use environ::Environ;
 use environ::default_env;
+use environ::Environ;
 
 mod parser;
 use parser::parse;
 use parser::parse_eval;
 use parser::parse_list_of_floats;
 
-
+mod evaluate;
 
 #[derive(Debug)]
 enum RispError {
     Reason(String),
 }
 
-
 #[derive(Clone)]
 enum Expr {
+    Bool(bool),
     Symbol(String),
     Number(f64),
     List(Vec<Expr>),
-      Func(fn(&[Expr]) -> Result<Expr, RispError>), // bam
+    Func(fn(&[Expr]) -> Result<Expr, RispError>),
+    Lambda(RLambda),
+}
+
+#[derive(Clone)]
+struct RLambda {
+    params_exp: Rc<Expr>,
+    body_exp: Rc<Expr>,
 }
 
 impl fmt::Display for Expr {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use Expr::*;
         let str = match self {
-      Expr::Symbol(s) => s.clone(),
-      Expr::Number(n) => n.to_string(),
-      Expr::List(list) => {
-        let xs: Vec<String> = list
-          .iter()
-          .map(|x| x.to_string())
-          .collect();
+            Bool(a) => a.to_string(),
+            Symbol(s) => s.clone(),
+            Number(n) => n.to_string(),
+            List(list) => {
+                let xs: Vec<String> = list.iter().map(|x| x.to_string()).collect();
                 format!("({})", xs.join(","))
-      },
-      Expr::Func(_) => "Function {}".to_string(),
+            }
+            Func(_) => "Function {}".to_string(),
+            Lambda(_) => "Lambda {}".to_string(),
         };
 
         write!(f, "{}", str)
     }
 }
 
-
-
-fn eval(exp: &Expr, env: &mut Environ) -> Result<Expr, RispError> {
-  match exp {
-    Expr::Symbol(k) =>
-        env.data.get(k)
-        .ok_or(
-          RispError::Reason(
-            format!("unexpected symbol k='{}'", k)
-          )
-        )
-        .map(|x| x.clone())
-    ,
-    Expr::Number(_a) => Ok(exp.clone()),
-    Expr::List(list) => {
-      let first_form = list
-        .first()
-        .ok_or(RispError::Reason("expected a non-empty list".to_string()))?;
-      let arg_forms = &list[1..];
-      let first_eval = eval(first_form, env)?;
-      match first_eval {
-        Expr::Func(f) => {
-          let args_eval = arg_forms
-            .iter()
-            .map(|x| eval(x, env))
-            .collect::<Result<Vec<Expr>, RispError>>();
-          f(&args_eval?)
-        },
-        _ => Err(
-          RispError::Reason("first form must be a function".to_string())
-        ),
-      }
-    },
-    Expr::Func(_) => Err(
-      RispError::Reason("unexpected form".to_string())
-    ),
-  }
-}
-
-
-
 fn read_seq<'a>(tokens: &'a [String]) -> Result<(Expr, &'a [String]), RispError> {
     let mut res: Vec<Expr> = vec![];
     let mut xs = tokens;
     loop {
         let (next_token, rest) = xs
             .split_first()
-      .ok_or(RispError::Reason("could not find closing `)`".to_string()))
-      ?;
+            .ok_or(RispError::Reason("could not find closing `)`".to_string()))?;
         if next_token == ")" {
-      return Ok((Expr::List(res), rest)) // skip `)`, head to the token after
+            return Ok((Expr::List(res), rest)); // skip `)`, head to the token after
         }
         let (exp, new_xs) = parse(&xs)?;
         res.push(exp);
@@ -105,12 +72,11 @@ fn read_seq<'a>(tokens: &'a [String]) -> Result<(Expr, &'a [String]), RispError>
     }
 }
 
-
-
 fn slurp_expr() -> String {
     let mut expr = String::new();
 
-  io::stdin().read_line(&mut expr)
+    io::stdin()
+        .read_line(&mut expr)
         .expect("Failed to read line");
 
     expr

src/parser.rs

@@ -1,43 +1,31 @@
-use crate::RispError;
-use crate::Expr;
-use crate::eval;
-use crate::Environ;
+use crate::evaluate::eval;
 use crate::read_seq;
+use crate::Environ;
+use crate::Expr;
 use crate::ParseFloatError;
+use crate::RispError;
 
-pub 
-
-fn tokenize(expr: String) -> Vec<String> {
-    expr
-    .replace("(", " ( ")
+pub fn tokenize(expr: String) -> Vec<String> {
+    expr.replace("(", " ( ")
         .replace(")", " ) ")
         .split_whitespace()
         .map(|x| x.to_string())
         .collect()
 }
 
-pub 
-
-fn parse<'a>(tokens: &'a [String]) -> Result<(Expr, &'a [String]), RispError>{
-    let (token, rest) = tokens.split_first()
-    .ok_or(
-        RispError::Reason("Could not get token".to_string())
-    )?;
+pub fn parse<'a>(tokens: &'a [String]) -> Result<(Expr, &'a [String]), RispError> {
+    let (token, rest) = tokens
+        .split_first()
+        .ok_or(RispError::Reason("Could not get token".to_string()))?;
     match &token[..] {
-        "("=>{read_seq(rest)}
+        "(" => read_seq(rest),
         ")" => Err(RispError::Reason("unexpected `)`".to_string())),
-        _ => Ok((parse_atom(token), rest))
+        _ => Ok((parse_atom(token), rest)),
     }
 }
 
-
-pub 
-
-fn parse_list_of_floats(args: &[Expr]) -> Result<Vec<f64>, RispError> {
-  args
-    .iter()
-    .map(|x| parse_single_float(x))
-    .collect()
+pub fn parse_list_of_floats(args: &[Expr]) -> Result<Vec<f64>, RispError> {
+    args.iter().map(|x| parse_single_float(x)).collect()
 }
 
 fn parse_single_float(exp: &Expr) -> Result<f64, RispError> {
@@ -47,17 +35,21 @@ fn parse_single_float(exp: &Expr) -> Result<f64, RispError> {
     }
 }
 
-
-
-
 fn parse_atom(token: &str) -> Expr {
+    use Expr::*;
+    match token.as_ref() {
+        "true" => Bool(true),
+        "false" => Bool(false),
+        _ => {
             let potential_float: Result<f64, ParseFloatError> = token.parse();
             match potential_float {
-    Ok(v) => Expr::Number(v),
-    Err(_) => Expr::Symbol(token.to_string().clone())
+                Ok(v) => Number(v),
+                Err(_) => Symbol(token.to_string().clone()),
             }
-}pub 
-fn parse_eval(expr: String, env: &mut Environ) -> Result<Expr, RispError> {
+        }
+    }
+}
+pub fn parse_eval(expr: String, env: &mut Environ) -> Result<Expr, RispError> {
     let (parsed_exp, _) = parse(&tokenize(expr))?;
     let evaled_exp = eval(&parsed_exp, env)?;