schala/rukka/src/lib.rs

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#![feature(box_patterns)]
extern crate itertools;
extern crate schala_repl;
use itertools::Itertools;
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use schala_repl::{ProgrammingLanguageInterface, EvalOptions, UnfinishedComputation, FinishedComputation};
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use std::iter::Peekable;
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use std::vec::IntoIter;
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use std::str::Chars;
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use std::collections::HashMap;
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pub struct EvaluatorState {
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binding_stack: Vec<HashMap<String, Sexp>>
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}
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impl EvaluatorState {
fn new() -> EvaluatorState {
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use self::Sexp::Primitive;
use self::PrimitiveFn::*;
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let mut default_map = HashMap::new();
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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));
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default_map.insert(format!("display"), Primitive(Display));
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EvaluatorState {
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binding_stack: vec![default_map],
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}
}
fn set_var(&mut self, var: String, value: Sexp) {
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let binding = self.binding_stack.last_mut().unwrap();
binding.insert(var, value);
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}
fn get_var(&self, var: &str) -> Option<&Sexp> {
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for bindings in self.binding_stack.iter().rev() {
match bindings.get(var) {
Some(x) => return Some(x),
None => (),
}
}
None
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}
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fn push_env(&mut self) {
self.binding_stack.push(HashMap::new());
}
fn pop_env(&mut self) {
self.binding_stack.pop();
}
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}
pub struct Rukka {
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state: EvaluatorState
}
impl Rukka {
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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")
}
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fn execute_pipeline(&mut self, input: &str, _eval_options: &EvalOptions) -> FinishedComputation {
let mut output = UnfinishedComputation::default();
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let sexps = match read(input) {
Err(err) => {
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return output.finish(Err(format!("Error: {}", err)));
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},
Ok(sexps) => sexps
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};
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let output_str: String = sexps.into_iter().enumerate().map(|(i, sexp)| {
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match self.state.eval(sexp) {
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Ok(result) => format!("{}: {}", i, result.print()),
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Err(err) => format!("{} Error: {}", i, err),
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}
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}).intersperse(format!("\n")).collect();
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output.finish(Ok(output_str))
}
}
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impl EvaluatorState {
fn eval(&mut self, expr: Sexp) -> Result<Sexp, String> {
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use self::Sexp::*;
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Ok(match expr {
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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)),
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},
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expr @ Primitive(_) => expr,
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expr @ FnLiteral { .. } => expr,
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expr @ StringAtom(_) => expr,
expr @ NumberAtom(_) => expr,
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expr @ BoolAtom(_) => expr,
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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)?
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}
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},
Nil => Nil,
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})
}
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fn eval_special_form(&mut self, form: &str, operands: Sexp) -> Result<Sexp, String> {
use self::Sexp::*;
Ok(match form {
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"quote" => match operands {
Cons(box quoted, box Nil) => quoted,
_ => return Err(format!("Bad syntax in quote")),
},
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"eq?" => match operands {//TODO make correct
Cons(box lhs, box Cons(box rhs, _)) => BoolAtom(lhs == rhs),
_ => BoolAtom(true),
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},
"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 {
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Cons(_, _) => BoolAtom(false),
_ => BoolAtom(true),
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},
"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 {
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Cons(box mut paramlist, box Cons(box formalexp, box Nil)) => {
let mut formal_params = vec![];
{
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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,
}
}
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}
FnLiteral {
formal_params,
body: Box::new(formalexp)
}
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},
_ => 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"))
},
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s => return Err(format!("Non-existent special form {}; this should never happen", s)),
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})
}
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fn apply(&mut self, function: Sexp, operands: Sexp) -> Result<Sexp, String> {
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use self::Sexp::*;
match function {
FnLiteral { formal_params, body } => {
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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
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},
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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"))
}
}
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prim.apply(evaled_operands)
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}
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_ => return Err(format!("Bad type to apply")),
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}
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}
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}
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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();
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while let Some(_) = tokens.peek() {
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sexps.push(parse(&mut tokens)?);
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}
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Ok(sexps)
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}
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#[derive(Debug)]
enum Token {
LParen,
RParen,
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Quote,
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Word(String),
StringLiteral(String),
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NumLiteral(u64),
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}
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//TODO make this notion of Eq more sophisticated
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#[derive(Debug, PartialEq, Clone)]
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enum Sexp {
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SymbolAtom(String),
StringAtom(String),
NumberAtom(u64),
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BoolAtom(bool),
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Cons(Box<Sexp>, Box<Sexp>),
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Nil,
FnLiteral {
formal_params: Vec<String>,
body: Box<Sexp>
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},
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Primitive(PrimitiveFn)
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}
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#[derive(Debug, PartialEq, Clone)]
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enum PrimitiveFn {
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Plus, Minus, Mult, Div, Mod, Greater, Less, GreaterThanOrEqual, LessThanOrEqual, Display
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}
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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 {
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Display => {
for arg in evaled_operands {
print!("{}\n", arg.print());
}
Nil
},
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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)),
})
}
}
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impl Sexp {
fn print(&self) -> String {
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use self::Sexp::*;
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match self {
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&BoolAtom(true) => format!("#t"),
&BoolAtom(false) => format!("#f"),
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&SymbolAtom(ref sym) => format!("{}", sym),
&StringAtom(ref s) => format!("\"{}\"", s),
&NumberAtom(ref n) => format!("{}", n),
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&Cons(ref car, ref cdr) => format!("({} . {})", car.print(), cdr.print()),
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&Nil => format!("()"),
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&FnLiteral { ref formal_params, .. } => format!("<lambda {:?}>", formal_params),
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&Primitive(ref sym) => format!("<primitive \"{:?}\">", sym),
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}
}
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fn truthy(&self) -> bool {
use self::Sexp::*;
match self {
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&BoolAtom(false) => false,
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_ => true
}
}
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}
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fn tokenize(input: &mut Peekable<Chars>) -> Vec<Token> {
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use self::Token::*;
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let mut tokens = Vec::new();
loop {
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match input.next() {
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None => break,
Some('(') => tokens.push(LParen),
Some(')') => tokens.push(RParen),
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Some('\'') => tokens.push(Quote),
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Some(c) if c.is_whitespace() => continue,
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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));
},
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Some('"') => {
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let string: String = input.scan(false, |escape, cur_char| {
let seen_escape = *escape;
*escape = cur_char == '\\' && !seen_escape;
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match (cur_char, seen_escape) {
('"', false) => None,
('\\', false) => Some(None),
(c, _) => Some(Some(c))
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}
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}).filter_map(|x| x).collect();
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tokens.push(StringLiteral(string));
}
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Some(c) => {
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let sym: String = input.peeking_take_while(|next| {
match *next {
'(' | ')' => false,
c if c.is_whitespace() => false,
_ => true
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}
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}).collect();
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tokens.push(Word(format!("{}{}", c, sym)));
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}
}
}
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tokens
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}
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fn parse(tokens: &mut Peekable<IntoIter<Token>>) -> Result<Sexp, String> {
use self::Token::*;
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use self::Sexp::*;
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match tokens.next() {
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Some(Word(ref s)) if s == "#f" => Ok(BoolAtom(false)),
Some(Word(ref s)) if s == "#t" => Ok(BoolAtom(true)),
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Some(Word(s)) => Ok(SymbolAtom(s)),
Some(StringLiteral(s)) => Ok(StringAtom(s)),
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Some(LParen) => parse_sexp(tokens),
Some(RParen) => Err(format!("Unexpected ')'")),
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Some(Quote) => {
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let quoted = parse(tokens)?;
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Ok(Cons(Box::new(SymbolAtom(format!("quote"))), Box::new(Cons(Box::new(quoted), Box::new(Nil)))))
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},
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Some(NumLiteral(n)) => Ok(NumberAtom(n)),
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None => Err(format!("Unexpected end of input")),
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}
}
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fn parse_sexp(tokens: &mut Peekable<IntoIter<Token>>) -> Result<Sexp, String> {
use self::Token::*;
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use self::Sexp::*;
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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!()
};
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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;
}
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}
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}
}
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Ok(cell)
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}