rust-parser-combinator/src/lib.rs

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

pub use parser::{ParseResult, Parser};

#[cfg(test)]
mod tests {
    use super::*;
    use crate::choice::choice;
    use crate::combinators::repeated;
    use crate::primitives::{any_char, literal, literal_char, one_of, pred};
    use crate::sequence::seq;
    use std::collections::HashMap;

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

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

    trait JsonParser<'a, T>: Parser<&'a str, T, &'a str> {}
    impl<'a, T, P> JsonParser<'a, T> for P where P: Parser<&'a str, T, &'a str> {}

    fn json_null<'a>() -> impl JsonParser<'a, JsonValue> {
        literal("null").to(JsonValue::Null)
    }
    fn json_bool<'a>() -> impl JsonParser<'a, JsonValue> {
        choice((
            literal("true").to(JsonValue::Bool(true)),
            literal("false").to(JsonValue::Bool(false)),
        ))
    }

    fn json_number() -> impl JsonParser<'static, JsonValue> {
        let digit = || one_of("1234567890");
        let digits = || repeated(digit()).at_least(1);

        let json_number_inner = choice((
            seq((digits(), literal(".").ignore_then(digits()).optional())).map(
                |(mut digits, maybe_decimal)| {
                    if let Some(decimal_digits) = maybe_decimal {
                        digits.push(".");
                        digits.extend(decimal_digits.into_iter());
                    }
                    digits.into_iter().collect::<String>()
                },
            ),
            literal(".").ignore_then(digits()).map(|decimal_digits| {
                let mut d = vec!["."];
                d.extend(decimal_digits.into_iter());
                d.into_iter().collect::<String>()
            }),
        ))
        .map(|digits| digits.parse::<f64>().unwrap());

        literal("-")
            .optional()
            .then(json_number_inner)
            .map(|(maybe_sign, mut val)| {
                if maybe_sign.is_some() {
                    val *= -1.0;
                }
                JsonValue::Num(val)
            })
    }

    fn json_string<'a>() -> impl JsonParser<'a, JsonValue> {
        seq((
            literal_char('"'),
            pred(any_char, |ch| *ch != '"'),
            literal_char('"'),
        ))
        .map(|(_, s, _)| JsonValue::Str(s.to_string()))
    }

    fn whitespace() -> impl JsonParser<'static, ()> {
        repeated(literal_char(' ')).to(())
    }

    fn json_array() -> impl JsonParser<'static, JsonValue> {
        let val = whitespace().ignore_then(json_value()).then_ignore(whitespace());

        literal_char('[')
            .ignore_then(repeated(val))
            .then_ignore(literal_char(']'))
            .map(JsonValue::Array)
    }

    fn json_value() -> impl JsonParser<'static, JsonValue> {
        choice((json_null(), json_bool(), json_number(), json_string()))
    }

    #[test]
    fn parse_json() {
        assert_eq!(
            json_number().parse("-383").unwrap().0,
            JsonValue::Num(-383f64)
        );
        assert_eq!(
            json_number().parse("-.383").unwrap().0,
            JsonValue::Num(-0.383)
        );
        assert_eq!(
            json_number().parse(".383").unwrap().0,
            JsonValue::Num(0.383)
        );
        assert_eq!(
            json_number().parse("-1.383").unwrap().0,
            JsonValue::Num(-1.383)
        );

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