schala/rukka/src/lib.rs
2018-07-26 00:52:46 -07:00

436 lines
13 KiB
Rust

#![feature(box_patterns)]
extern crate itertools;
extern crate schala_repl;
use itertools::Itertools;
use schala_repl::{ProgrammingLanguageInterface, EvalOptions, UnfinishedComputation, FinishedComputation};
use std::iter::Peekable;
use std::vec::IntoIter;
use std::str::Chars;
use std::collections::HashMap;
pub struct EvaluatorState {
binding_stack: Vec<HashMap<String, Sexp>>
}
impl EvaluatorState {
fn new() -> EvaluatorState {
use self::Sexp::Primitive;
use self::PrimitiveFn::*;
let mut default_map = HashMap::new();
default_map.insert(format!("+"), Primitive(Plus));
default_map.insert(format!("-"), Primitive(Minus));
default_map.insert(format!("*"), Primitive(Mult));
default_map.insert(format!("/"), Primitive(Div));
default_map.insert(format!("%"), Primitive(Mod));
default_map.insert(format!(">"), Primitive(Greater));
default_map.insert(format!("<"), Primitive(Less));
default_map.insert(format!("<="), Primitive(LessThanOrEqual));
default_map.insert(format!(">="), Primitive(GreaterThanOrEqual));
default_map.insert(format!("display"), Primitive(Display));
EvaluatorState {
binding_stack: vec![default_map],
}
}
fn set_var(&mut self, var: String, value: Sexp) {
let binding = self.binding_stack.last_mut().unwrap();
binding.insert(var, value);
}
fn get_var(&self, var: &str) -> Option<&Sexp> {
for bindings in self.binding_stack.iter().rev() {
match bindings.get(var) {
Some(x) => return Some(x),
None => (),
}
}
None
}
fn push_env(&mut self) {
self.binding_stack.push(HashMap::new());
}
fn pop_env(&mut self) {
self.binding_stack.pop();
}
}
pub struct Rukka {
state: EvaluatorState
}
impl Rukka {
pub fn new() -> Rukka { Rukka { state: EvaluatorState::new() } }
}
impl ProgrammingLanguageInterface for Rukka {
fn get_language_name(&self) -> String {
"Rukka".to_string()
}
fn get_source_file_suffix(&self) -> String {
format!("rukka")
}
fn execute_pipeline(&mut self, input: &str, _eval_options: &EvalOptions) -> FinishedComputation {
let output = UnfinishedComputation::default();
let sexps = match read(input) {
Err(err) => {
return output.finish(Err(format!("Error: {}", err)));
},
Ok(sexps) => sexps
};
let output_str: String = sexps.into_iter().enumerate().map(|(i, sexp)| {
match self.state.eval(sexp) {
Ok(result) => format!("{}: {}", i, result.print()),
Err(err) => format!("{} Error: {}", i, err),
}
}).intersperse(format!("\n")).collect();
output.finish(Ok(output_str))
}
}
impl EvaluatorState {
fn eval(&mut self, expr: Sexp) -> Result<Sexp, String> {
use self::Sexp::*;
Ok(match expr {
SymbolAtom(ref sym) => match self.get_var(sym) {
Some(ref sexp) => {
let q: &Sexp = sexp; //WTF? if I delete this line, the copy doesn't work??
q.clone() //TODO make this not involve a clone
},
None => return Err(format!("Variable {} not bound", sym)),
},
expr @ Primitive(_) => expr,
expr @ FnLiteral { .. } => expr,
expr @ StringAtom(_) => expr,
expr @ NumberAtom(_) => expr,
expr @ BoolAtom(_) => expr,
Cons(box operator, box operands) => match operator {
SymbolAtom(ref sym) if match &sym[..] {
"quote" | "eq?" | "cons" | "car" | "cdr" | "atom?" | "define" | "lambda" | "if" | "cond" => true, _ => false
} => self.eval_special_form(sym, operands)?,
_ => {
let evaled = self.eval(operator)?;
self.apply(evaled, operands)?
}
},
Nil => Nil,
})
}
fn eval_special_form(&mut self, form: &str, operands: Sexp) -> Result<Sexp, String> {
use self::Sexp::*;
Ok(match form {
"quote" => match operands {
Cons(box quoted, box Nil) => quoted,
_ => return Err(format!("Bad syntax in quote")),
},
"eq?" => match operands {//TODO make correct
Cons(box lhs, box Cons(box rhs, _)) => BoolAtom(lhs == rhs),
_ => BoolAtom(true),
},
"cons" => match operands {
Cons(box cadr, box Cons(box caddr, box Nil)) => {
let newl = self.eval(cadr)?;
let newr = self.eval(caddr)?;
Cons(Box::new(newl), Box::new(newr))
},
_ => return Err(format!("Bad arguments for cons")),
},
"car" => match operands {
Cons(box car, _) => car,
_ => return Err(format!("called car with a non-pair argument")),
},
"cdr" => match operands {
Cons(_, box cdr) => cdr,
_ => return Err(format!("called cdr with a non-pair argument")),
},
"atom?" => match operands {
Cons(_, _) => BoolAtom(false),
_ => BoolAtom(true),
},
"define" => match operands {
Cons(box SymbolAtom(sym), box Cons(box expr, box Nil)) => {
let evaluated = self.eval(expr)?;
self.set_var(sym, evaluated);
Nil
},
_ => return Err(format!("Bad assignment")),
}
"lambda" => match operands {
Cons(box mut paramlist, box Cons(box formalexp, box Nil)) => {
let mut formal_params = vec![];
{
let mut ptr = &paramlist;
loop {
match ptr {
&Cons(ref arg, ref rest) => {
if let SymbolAtom(ref sym) = **arg {
formal_params.push(sym.clone());
ptr = rest;
} else {
return Err(format!("Bad lambda format"));
}
},
_ => break,
}
}
}
FnLiteral {
formal_params,
body: Box::new(formalexp)
}
},
_ => return Err(format!("Bad lambda expression")),
},
"if" => match operands {
Cons(box test, box body) => {
let truth_value = test.truthy();
match (truth_value, body) {
(true, Cons(box consequent, _)) => consequent,
(false, Cons(_, box Cons(box alternative, _))) => alternative,
_ => return Err(format!("Bad if expression"))
}
},
_ => return Err(format!("Bad if expression"))
},
s => return Err(format!("Non-existent special form {}; this should never happen", s)),
})
}
fn apply(&mut self, function: Sexp, operands: Sexp) -> Result<Sexp, String> {
use self::Sexp::*;
match function {
FnLiteral { formal_params, body } => {
self.push_env();
let mut cur = operands;
for param in formal_params {
match cur {
Cons(box arg, box rest) => {
cur = rest;
self.set_var(param, arg);
},
_ => return Err(format!("Bad argument for function application")),
}
}
let result = self.eval(*body);
self.pop_env();
result
},
Primitive(prim) => {
let mut evaled_operands = Vec::new();
let mut cur_operand = operands;
loop {
match cur_operand {
Nil => break,
Cons(box l, box rest) => {
evaled_operands.push(self.eval(l)?);
cur_operand = rest;
},
_ => return Err(format!("Bad operands list"))
}
}
prim.apply(evaled_operands)
}
_ => return Err(format!("Bad type to apply")),
}
}
}
fn read(input: &str) -> Result<Vec<Sexp>, String> {
let mut chars: Peekable<Chars> = input.chars().peekable();
let mut tokens = tokenize(&mut chars).into_iter().peekable();
let mut sexps = Vec::new();
while let Some(_) = tokens.peek() {
sexps.push(parse(&mut tokens)?);
}
Ok(sexps)
}
#[derive(Debug)]
enum Token {
LParen,
RParen,
Quote,
Word(String),
StringLiteral(String),
NumLiteral(u64),
}
//TODO make this notion of Eq more sophisticated
#[derive(Debug, PartialEq, Clone)]
enum Sexp {
SymbolAtom(String),
StringAtom(String),
NumberAtom(u64),
BoolAtom(bool),
Cons(Box<Sexp>, Box<Sexp>),
Nil,
FnLiteral {
formal_params: Vec<String>,
body: Box<Sexp>
},
Primitive(PrimitiveFn)
}
#[derive(Debug, PartialEq, Clone)]
enum PrimitiveFn {
Plus, Minus, Mult, Div, Mod, Greater, Less, GreaterThanOrEqual, LessThanOrEqual, Display
}
impl PrimitiveFn {
fn apply(&self, evaled_operands: Vec<Sexp>) -> Result<Sexp, String> {
use self::Sexp::*;
use self::PrimitiveFn::*;
let op = self.clone();
Ok(match op {
Display => {
for arg in evaled_operands {
print!("{}\n", arg.print());
}
Nil
},
Plus | Mult => {
let mut result = match op { Plus => 0, Mult => 1, _ => unreachable!() };
for arg in evaled_operands {
if let NumberAtom(n) = arg {
if let Plus = op {
result += n;
} else if let Mult = op {
result *= n;
}
} else {
return Err(format!("Bad operand: {:?}", arg));
}
}
NumberAtom(result)
},
op => return Err(format!("Primitive op {:?} not implemented", op)),
})
}
}
impl Sexp {
fn print(&self) -> String {
use self::Sexp::*;
match self {
&BoolAtom(true) => format!("#t"),
&BoolAtom(false) => format!("#f"),
&SymbolAtom(ref sym) => format!("{}", sym),
&StringAtom(ref s) => format!("\"{}\"", s),
&NumberAtom(ref n) => format!("{}", n),
&Cons(ref car, ref cdr) => format!("({} . {})", car.print(), cdr.print()),
&Nil => format!("()"),
&FnLiteral { ref formal_params, .. } => format!("<lambda {:?}>", formal_params),
&Primitive(ref sym) => format!("<primitive \"{:?}\">", sym),
}
}
fn truthy(&self) -> bool {
use self::Sexp::*;
match self {
&BoolAtom(false) => false,
_ => true
}
}
}
fn tokenize(input: &mut Peekable<Chars>) -> Vec<Token> {
use self::Token::*;
let mut tokens = Vec::new();
loop {
match input.next() {
None => break,
Some('(') => tokens.push(LParen),
Some(')') => tokens.push(RParen),
Some('\'') => tokens.push(Quote),
Some(c) if c.is_whitespace() => continue,
Some(c) if c.is_numeric() => {
let tok: String = input.peeking_take_while(|next| next.is_numeric()).collect();
let n: u64 = format!("{}{}", c, tok).parse().unwrap();
tokens.push(NumLiteral(n));
},
Some('"') => {
let string: String = input.scan(false, |escape, cur_char| {
let seen_escape = *escape;
*escape = cur_char == '\\' && !seen_escape;
match (cur_char, seen_escape) {
('"', false) => None,
('\\', false) => Some(None),
(c, _) => Some(Some(c))
}
}).filter_map(|x| x).collect();
tokens.push(StringLiteral(string));
}
Some(c) => {
let sym: String = input.peeking_take_while(|next| {
match *next {
'(' | ')' => false,
c if c.is_whitespace() => false,
_ => true
}
}).collect();
tokens.push(Word(format!("{}{}", c, sym)));
}
}
}
tokens
}
fn parse(tokens: &mut Peekable<IntoIter<Token>>) -> Result<Sexp, String> {
use self::Token::*;
use self::Sexp::*;
match tokens.next() {
Some(Word(ref s)) if s == "#f" => Ok(BoolAtom(false)),
Some(Word(ref s)) if s == "#t" => Ok(BoolAtom(true)),
Some(Word(s)) => Ok(SymbolAtom(s)),
Some(StringLiteral(s)) => Ok(StringAtom(s)),
Some(LParen) => parse_sexp(tokens),
Some(RParen) => Err(format!("Unexpected ')'")),
Some(Quote) => {
let quoted = parse(tokens)?;
Ok(Cons(Box::new(SymbolAtom(format!("quote"))), Box::new(Cons(Box::new(quoted), Box::new(Nil)))))
},
Some(NumLiteral(n)) => Ok(NumberAtom(n)),
None => Err(format!("Unexpected end of input")),
}
}
fn parse_sexp(tokens: &mut Peekable<IntoIter<Token>>) -> Result<Sexp, String> {
use self::Token::*;
use self::Sexp::*;
let mut cell = Nil;
{
let mut cell_ptr = &mut cell;
loop {
match tokens.peek() {
None => return Err(format!("Unexpected end of input")),
Some(&RParen) => {
tokens.next();
break;
},
_ => {
let current = parse(tokens)?;
let new_cdr = Cons(Box::new(current), Box::new(Nil));
match cell_ptr {
&mut Cons(_, ref mut cdr) => **cdr = new_cdr,
&mut Nil => *cell_ptr = new_cdr,
_ => unreachable!()
};
let old_ptr = cell_ptr;
let new_ptr: &mut Sexp = match old_ptr { &mut Cons(_, ref mut cdr) => cdr, _ => unreachable!() } as &mut Sexp;
cell_ptr = new_ptr;
}
}
}
}
Ok(cell)
}