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::{one_or_more, zero_or_more};
    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>),
    }

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

        let digit = || one_of("1234567890");
        assert_eq!(digit().parse("3"), Ok(("3", "")));

        let json_number_inner = choice((
            seq((
                one_or_more(digit()),
                literal(".").then(zero_or_more(digit())).optional(),
            ))
            .map(|(mut digits, maybe_more)| {
                if let Some((point, more)) = maybe_more {
                    digits.push(point);
                    digits.extend(more.into_iter());
                }
                digits.into_iter().collect::<String>()
            }),
            seq((literal("."), one_or_more(digit()))).map(|(_point, digits)| {
                let mut d = vec!["."];
                d.extend(digits.into_iter());
                d.into_iter().collect::<String>()
            }),
        ))
        .map(|digits| digits.parse::<f64>().unwrap());

        let json_number =
            literal("-")
                .optional()
                .then(json_number_inner)
                .map(|(maybe_sign, val)| {
                    if maybe_sign.is_some() {
                        val * -1.0
                    } else {
                        val
                    }
                });

        assert_eq!(json_number.parse("-383").unwrap().0, -383f64);
        assert_eq!(json_number.parse("-.383").unwrap().0, -0.383);
        assert_eq!(json_number.parse(".383").unwrap().0, 0.383);
        assert_eq!(json_number.parse("-1.383").unwrap().0, -1.383);

        let json_string = seq((
            literal_char('"'),
            pred(any_char, |ch| *ch != '"'),
            literal_char('"'),
        ))
        .map(|(_, s, _)| JsonValue::Str(s.to_string()));

        let json_value = choice((json_null, json_bool, json_string));

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