Crate combine [] [src]

This crate contains parser combinators, roughly based on the Haskell library parsec.

A parser in this library can be described as a function which takes some input and if it is succesful, returns a value together with the remaining input. A parser combinator is a function which takes one or more parsers and returns a new parser. For instance the many parser can be used to convert a parser for single digits into one that parses multiple digits. By modeling parsers in this way it becomes simple to compose complex parsers in an almost declarative way.

Overview

combine limits itself to creating LL(1) parsers (it is possible to opt-in to LL(k) parsing using the try combinator) which makes the parsers easy to reason about in both function and performance while sacrificing some generality. In addition to you being able to reason better about the parsers you construct combine the library also takes the knowledge of being an LL parser and uses it to automatically construct good error messages.

extern crate combine;
use combine::{Parser, State};
use combine::char::{digit, letter};
const MSG: &'static str = r#"Parse error at line: 1, column: 1
Unexpected `|`
Expected `digit` or `letter`
"#;

fn main() {
    // Wrapping a `&str` with `State` provides automatic line and column tracking. If `State`
    // was not used the positions would instead only be pointers into the `&str`
    if let Err(err) = digit().or(letter()).parse(State::new("|")) {
        assert_eq!(MSG, format!("{}", err));
    }
}

This library currently contains five modules:

Examples

extern crate combine;
use combine::char::{spaces, digit, char};
use combine::{many1, sep_by, Parser, ParseError};

fn main() {
    //Parse spaces first and use the with method to only keep the result of the next parser
    let integer = spaces()
        //parse a string of digits into an i32
        .with(many1(digit()).map(|string: String| string.parse::<i32>().unwrap()));

    //Parse integers separated by commas, skipping whitespace
    let mut integer_list = sep_by(integer, spaces().skip(char(',')));

    //Call parse with the input to execute the parser
    let input = "1234, 45,78";
    let result: Result<(Vec<i32>, &str), ParseError<&str>> = integer_list.parse(input);
    match result {
        Ok((value, _remaining_input)) => println!("{:?}", value),
        Err(err) => println!("{}", err)
    }
}

If we need a parser that is mutually recursive we can define a free function which internally can in turn be used as a parser by using the parser function which turns a function with the correct signature into a parser. In this case we define expr to work on any type of Stream which is combine's way of abstracting over different data sources such as array slices, string slices, iterators etc. If instead you would only need to parse string already in memory you could define expr as fn expr(input: &str) -> ParseResult<Expr, &str>

extern crate combine;
use combine::char::{char, letter, spaces};
use combine::{between, many1, parser, sep_by, Parser};
use combine::primitives::{State, Stream, ParseResult};

#[derive(Debug, PartialEq)]
enum Expr {
    Id(String),
    Array(Vec<Expr>),
    Pair(Box<Expr>, Box<Expr>)
}

fn expr<I>(input: I) -> ParseResult<Expr, I>
    where I: Stream<Item=char>
{
    let word = many1(letter());

    //Creates a parser which parses a char and skips any trailing whitespace
    let lex_char = |c| char(c).skip(spaces());

    let comma_list = sep_by(parser(expr::<I>), lex_char(','));
    let array = between(lex_char('['), lex_char(']'), comma_list);

    //We can use tuples to run several parsers in sequence
    //The resulting type is a tuple containing each parsers output
    let pair = (lex_char('('),
                parser(expr::<I>),
                lex_char(','),
                parser(expr::<I>),
                lex_char(')'))
                   .map(|t| Expr::Pair(Box::new(t.1), Box::new(t.3)));

    word.map(Expr::Id)
        .or(array.map(Expr::Array))
        .or(pair)
        .skip(spaces())
        .parse_stream(input)
}

fn main() {
    let result = parser(expr)
        .parse("[[], (hello, world), [rust]]");
    let expr = Expr::Array(vec![
          Expr::Array(Vec::new())
        , Expr::Pair(Box::new(Expr::Id("hello".to_string())),
                     Box::new(Expr::Id("world".to_string())))
        , Expr::Array(vec![Expr::Id("rust".to_string())])
    ]);
    assert_eq!(result, Ok((expr, "")));
}

Modules

byte

Module containing parsers specialized on byte streams.

char

Module containing parsers specialized on character streams.

combinator

Module containing all specific parsers.

primitives

Module containing the primitive types which is used to create and compose more advanced parsers.

range

Module containing zero-copy parsers.

Macros

choice

Takes a number of parsers and tries to apply them each in order. Fails if all the parsers fails or if an applied parser consumes input before failing.

ctry

Structs

ParseError

Struct which hold information about an error that occurred at a specific position. Can hold multiple instances of Error if more that one error occurred in the same position.

State

The State<I> struct keeps track of the current position in the stream I using the Positioner trait to update the position.

Traits

Parser

By implementing the Parser trait a type says that it can be used to parse an input stream into the type Output.

Stream

A stream of tokens which can be duplicated

StreamOnce

StreamOnce represents a sequence of items that can be extracted one by one.

Functions

any

Parses any token.

between

Parses open followed by parser followed by close. Returns the value of parser.

chainl1

Parses p 1 or more times separated by op. The value returned is the one produced by the left associative application of the function returned by the parser op.

chainr1

Parses p one or more times separated by op. The value returned is the one produced by the right associative application of the function returned by op.

choice

Takes an array of parsers and tries to apply them each in order. Fails if all the parsers fails or if an applied parser consumes input before failing.

count

Parses parser from zero up to count times.

env_parser

Constructs a parser out of an environment and a function which needs the given environment to do the parsing. This is commonly useful to allow multiple parsers to share some environment while still allowing the parsers to be written in separate functions.

eof

Succeeds only if the stream is at end of input, fails otherwise.

from_iter

Converts an Iterator into a stream.

look_ahead

look_ahead(p) acts as p but doesn't consume input on success.

many

Parses p zero or more times returning a collection with the values from p.

many1

Parses p one or more times returning a collection with the values from p.

none_of

Extract one token and succeeds if it is not part of tokens.

not_followed_by

Succeeds only if parser fails. Never consumes any input.

one_of

Extract one token and succeeds if it is part of tokens.

optional

Parses parser and outputs Some(value) if it succeeds, None if it fails without consuming any input. Fails if parser fails after having consumed some input.

parser

Wraps a function, turning it into a parser.

position

Parser which just returns the current position in the stream.

satisfy

Parses a token and succeeds depending on the result of predicate.

satisfy_map

Parses a token and passes it to predicate. If predicate returns Some the parser succeeds and returns the value inside the Option. If predicate returns None the parser fails without consuming any input.

sep_by

Parses parser zero or more time separated by separator, returning a collection with the values from p.

sep_by1

Parses parser one or more time separated by separator, returning a collection with the values from p.

sep_end_by

Parses parser zero or more times separated and ended by separator, returning a collection with the values from p.

sep_end_by1

Parses parser one or more times separated and ended by separator, returning a collection with the values from p.

skip_many

Parses p zero or more times ignoring the result.

skip_many1

Parses p one or more times ignoring the result.

token

Parses a character and succeeds if the character is equal to c.

tokens

Parses multiple tokens.

try

try(p) behaves as p except it acts as if the parser hadn't consumed any input if p fails after consuming input.

unexpected

Always fails with message as an unexpected error. Never consumes any input.

value

Always returns the value v without consuming any input.

Type Definitions

ConsumedResult

A Result type which has the consumed status flattened into the result. Conversions to and from std::result::Result can be done using result.into() or From::from(result)

ParseResult

A type alias over the specific Result type used by parsers to indicate wether they were successful or not. O is the type that is output on success. I is the specific stream type used in the parser.