blob: d6bc1589893980244fc573ba405ea85c0efd651b [file] [log] [blame]
extern crate pest;
use std::io::{self, Write};
use pest::{state, ParseResult, Parser, ParserState};
use pest::error::Error;
use pest::iterators::Pairs;
#[allow(dead_code, non_camel_case_types)]
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
enum Rule {
expr,
paren,
paren_end
}
struct ParenParser;
impl Parser<Rule> for ParenParser {
fn parse(rule: Rule, input: &str) -> Result<Pairs<Rule>, Error<Rule>> {
fn expr(state: Box<ParserState<Rule>>) -> ParseResult<Box<ParserState<Rule>>> {
state.sequence(|s| s.repeat(|s| paren(s)).and_then(|s| s.end_of_input()))
}
fn paren(state: Box<ParserState<Rule>>) -> ParseResult<Box<ParserState<Rule>>> {
state.rule(Rule::paren, |s| {
s.sequence(|s| {
s.match_string("(")
.and_then(|s| {
s.optional(|s| {
s.sequence(|s| {
s.lookahead(true, |s| s.match_string("("))
.and_then(|s| s.repeat(|s| paren(s)))
})
})
})
.and_then(|s| s.rule(Rule::paren_end, |s| s.match_string(")")))
})
})
}
state(input, |state| match rule {
Rule::expr => expr(state),
Rule::paren => paren(state),
_ => unreachable!()
})
}
}
#[derive(Debug)]
struct Paren(Vec<Paren>);
fn expr(pairs: Pairs<Rule>) -> Vec<Paren> {
pairs
.filter(|p| p.as_rule() == Rule::paren)
.map(|p| Paren(expr(p.into_inner())))
.collect()
}
fn main() {
loop {
let mut line = String::new();
print!("> ");
io::stdout().flush().unwrap();
io::stdin().read_line(&mut line).unwrap();
line.pop();
match ParenParser::parse(Rule::expr, &line) {
Ok(pairs) => println!("{:?}", expr(pairs)),
Err(e) => println!("\n{}", e)
};
}
}