chomp1 0.3.4

A fast monadic-style parser combinator designed to work on stable Rust.
Documentation 
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use std::collections::HashMap;

use chomp1::ascii::{float, is_whitespace};
use chomp1::combinators::{or, sep_by};
use chomp1::parsers::Error as ChompError;
use chomp1::parsers::{any, scan, skip_while, string, token};
use chomp1::types::{Buffer, Input, ParseResult};

pub type Error = ChompError<u8>;

/// A JSON Value
#[derive(Clone, Debug, PartialEq)]
pub enum Value {
    Array(Vec<Value>),
    Number(f64),
    Object(HashMap<String, Value>),
    String(String),
    True,
    False,
    Null,
}

/// Parses a `Value` from the supplied input.
pub fn parse<I: Input<Token = u8>>(i: I) -> ParseResult<I, Value, Error> {
    skip_while(i, is_whitespace).then(|i| {
        or(
            i,
            |i| parse_object(i).map(Value::Object),
            |i| {
                or(
                    i,
                    |i| parse_array(i).map(Value::Array),
                    |i| {
                        or(
                            i,
                            |i| parse_string(i).map(Value::String),
                            |i| {
                                or(
                                    i,
                                    |i| float(i).map(Value::Number),
                                    |i| {
                                        or(
                                            i,
                                            |i| string(i, b"true").map(|_| Value::True),
                                            |i| {
                                                or(
                                                    i,
                                                    |i| string(i, b"false").map(|_| Value::False),
                                                    |i| {
                                                        or(
                                                            i,
                                                            |i| {
                                                                string(i, b"null")
                                                                    .map(|_| Value::Null)
                                                            },
                                                            |i| i.err(Error::unexpected()),
                                                        )
                                                    },
                                                )
                                            },
                                        )
                                    },
                                )
                            },
                        )
                    },
                )
            },
        )
    })
}

/// Parse a quoted string
fn parse_string<I: Input<Token = u8>>(i: I) -> ParseResult<I, String, Error> {
    token(i, b'"').then(|i| {
        scan(i, b'\0', |s, c| match (s, c) {
            (b'\\', b'"') => Some(c),
            (b'\\', b'\\') => Some(b'\0'), // null here because we need \\" to end
            (_, b'"') => None,
            (..) => Some(c),
        })
        .bind(|i, b| any(i).map(|_| unescape(b)))
    })
}

/// Unescape the contents of a quoted string.
fn unescape<B: Buffer<Token = u8>>(b: B) -> String {
    // FIXME: Implement escape sequence parsing
    unsafe { String::from_utf8_unchecked(b.to_vec()) }
}

/// Parses a JSON Object
fn parse_object<I: Input<Token = u8>>(i: I) -> ParseResult<I, HashMap<String, Value>, Error> {
    token(i, b'{').then(|i| {
        skip_while(i, is_whitespace).then(|i| {
            sep_by(i, parse_key_value, separator)
                .bind(|i, m| skip_while(i, is_whitespace).then(|i| token(i, b'}').map(|_| m)))
        })
    })
}

/// Whitespace + comma, separates key-value pairs in objects and values in
/// arrays
fn separator<I: Input<Token = u8>>(i: I) -> ParseResult<I, (), Error> {
    skip_while(i, is_whitespace).then(|i| token(i, b',').then(|i| skip_while(i, is_whitespace)))
}

/// Parses string-key: value
fn parse_key_value<I: Input<Token = u8>>(i: I) -> ParseResult<I, (String, Value), Error> {
    parse_string(i).bind(|i, s| {
        skip_while(i, is_whitespace).then(|i| {
            token(i, b':').then(|i| skip_while(i, is_whitespace).then(|i| parse(i).map(|v| (s, v))))
        })
    })
}

/// Parses a JSON array
fn parse_array<I: Input<Token = u8>>(i: I) -> ParseResult<I, Vec<Value>, Error> {
    token(i, b'[').then(|i| sep_by(i, parse, separator).bind(|i, v| token(i, b']').map(|_| v)))
}

use chomp1::combinators::many;
use chomp1::parse_only;

fn main() {
    let t: Vec<_> = parse_only(
        |i| many(i, parse),
        &b"{\"foo\": 1.23, \"some_more\": [1, 2, 3, \"lol\"]}"[..],
    )
    .unwrap();

    println!("{:?}", t);
}