rust-parser-combinator/src/lib.rs

#![feature(assert_matches)]
#![allow(dead_code)] //TODO eventually turn this off
mod bnf;
mod combinators;
mod parser;
mod primitives;
mod sequence;

use parser::{ParseResult, Parser};

fn choice<P1, P2, I, O, E>(parser1: P1, parser2: P2) -> impl Parser<I, O, E>
where
    P1: Parser<I, O, E>,
    P2: Parser<I, O, E>,
    I: Copy,
{
    move |input| match parser1.parse(input) {
        ok @ Ok(..) => ok,
        Err(_e) => parser2.parse(input),
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::combinators::one_or_more;
    use crate::primitives::literal;
    use std::assert_matches::assert_matches;
    use std::collections::HashMap;

    #[test]
    fn test_parsing() {
        let output = literal("a")("a yolo");
        assert_matches!(output.unwrap(), ("a", " yolo"));
    }

    #[test]
    fn test_choice() {
        let p = choice(literal("gnostika").to(1), one_or_more(literal(" ")).to(2));
        assert_eq!(p.parse("gnostika twentynine"), Ok((1, " twentynine")));
    }

    /*
     * JSON BNF
     * <JSON>     ::= <value>
    <value>    ::= <object> | <array> | <boolean> | <string> | <number> | <null>
    <array>    ::= "[" [<value>] {"," <value>}* "]"
    <object>   ::= "{" [<property>] {"," <property>}* "}"
    <property> ::= <string> ":" <value>
    */
    #[derive(Debug, Clone)]
    enum JsonValue {
        Null,
        Bool(bool),
        Str(String),
        Num(f64),
        Array(Vec<JsonValue>),
        Object(HashMap<String, JsonValue>),
    }

    #[test]
    fn parse_json() {
        let json_null = literal("null").to(JsonValue::Null);
        let json_true = literal("true").to(JsonValue::Bool(true));
        let json_false = literal("false").to(JsonValue::Bool(false));

        let json_value = choice(json_null, choice(json_true, json_false));

        assert_matches!(json_value.parse("true"), Ok((JsonValue::Bool(true), "")));
    }
}