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API Reference

Parser

import Parser from 'parser-lang';

The Parser is the primary class in ParserLang. A Parser is a wrapper around a function that does the parsing along with a variety of methods for combining the Parser instance with other Parsers.

constructor

Parser<A>(action: Context => Outcome<ParserResult<A>>)

A Parser is constructed by giving it a function that takes a Context to consume and returns an Outcome of a ParseResult.

An Outcome represents a Success or a Failure (for those coming from a functional background this is the Either type just with more clear names).

A ParseResult is an object of shape { value, ctx } that holds the resulting value along with the new Context.

import { Outcome } from 'parser-lang';

let p = new Parser(ctx => {
  return Outcome.of({
    value: true,
    ctx,
  });
});

parse

Parser<A>#parse(
  ctx: string | Array | Iterable | Context
): Outcome<ParseResult<A>>

Runs the wrapped action by first converting ctx to a Context.

tryParse

Parser<A>#tryParse(
  ctx: string | Array | Iterable | Context
): A

Runs the wrapped action by first converting ctx to a Context and then return its value (unwrapping the value from the Outcome and ParseResult). If the action returns a Failure outcome throws an Error.

Parser.failure('fail').tryParse('');
// throws Error('fail')

of

Parser.of(value: A): Parser<A>

Returns a parser that consumes nothing from the context and succeeds with value.

Parser.of(42).tryParse('123');
// 42

zero

Parser.zero(): Parser<>

Returns a parser that always results in a Failure outcome.

Parser.zero().tryParse('');
// throws Error

failure

Parser.failure(msg: string): Parser<>

Returns a parser that always results in a Failure outcome with msg as the failure message.

Parser.failure('a message').tryParse('');
// throws Error('a message')

map

Parser<A>#map(f: A => B): Parser<B>

Returns a parser that runs the first parser and then applies f to the resulting value.

Parser.of(2)
  .map(n => n * 10)
  .tryParse('');
// 20

ap

Parser<A>#ap(
  parser: Parser<A => B>
): Parser<B>

Returns a parser that runs the first parser and then runs parser to get the function A => B to apply to the result of the first parser.

chain

Parser<A>#chain(
  f: A => Parser<B>
): Parser<B>

Returns a parser that runs the first parser and then applies the value to f and returns the resulting parser.

or

Parser<A>#or(
  other: Parser<B>
): Parser<A | B>

Returns a parser that runs the first parser and if it results in a failure runs other.

Parser.zero()
  .or(Parser.of(1))
  .tryParse('');
// 1

alt

Alias for or.

then

Parser<A>#then(
  other: Parser<B>
): Parser<B>

Returns a parser that runs the first parser and then the second parser and returns the result of the second parser.

Parser.of(1)
  .then(Parser.of(2))
  .tryParse('');
// 2

skip

Parser<A>#skip(
  other: Parser<B>
): Parser<A>

Returns a parser that runs the first parser and then the second parser and returns the result of the first parser.

Parser.of(1)
  .skip(Parser.of(2))
  .tryParse('');
// 1

result

Parser<A>#result(
  value: B
): Parser<B>

Returns a parser that runs the first parser and then uses value as the result.

Parser.of(1)
  .result('a')
  .tryParse('');
// 'a'

many

Parser<A>#many(): Parser<A[]>

Returns a parser that matches this parser zero or more times and records the matched values in an array.

import { char } from 'parser-lang';

char('a')
  .many()
  .tryParse('aaa');
// ['a', 'a', 'a' ]
char('a')
  .many()
  .tryParse('bbb');
// []

atLeast

Parser<A>#atLeast(n: number): Parser<A[]>

Returns a parser that matches this parser at least n times and records the matched values in an array.

import { char } from 'parser-lang';

char('a')
  .atLeast(1)
  .tryParse('aaa');
// ['a', 'a', 'a' ]
char('a')
  .atLeast(1)
  .tryParse('bbb');
// throw Error

atMost

Parser<A>#atMost(n: number): Parser<A[]>

Returns a parser that matches this parser at most n times and records the matched values in an array.

import { char } from 'parser-lang';

char('a')
  .atMost(5)
  .tryParse('aaa');
// ['a', 'a', 'a' ]
char('a')
  .atMost(1)
  .tryParse('bbb');
// []
char('a')
  .atMost(1)
  .tryParse('aaa');
// throw Error

times

Parser<A>#times(n: number, max: number = n): Parser<A[]>

Returns a parser that matches this parser at least n but no more than max times and records the matched values in an array.

import { char } from 'parser-lang';

char('a')
  .times(3)
  .tryParse('aaa');
// ['a', 'a', 'a' ]
char('a')
  .times(1, 3)
  .tryParse('aa');
// ['a', 'a']
char('a')
  .times(1)
  .tryParse('bbb');
// throw Error

tie

Parser<A[]>#tie(
  sep: string = ''
): Parser<string>

Returns a parser that runs the first parser and then joins the resulting array by sep.

Parser.of(['a', 'b', 'c'])
  .tie()
  .tryParse('');
// 'abc'

Operators

succeed

succeed(value: A): Parser<A>

Returns a parser that always succeeds with value.

import { succeed } from 'parser-lang';

succeed('a').tryParse('');
// 'a'

empty

empty(): Parser<void>

Returns a parser that succeeds when the context is empty.

import { empty } from 'parser-lang';

empty().tryParse([]);
// undefined
empty().tryParse(['a']);
// throw Error

item

item(): Parser<A>

Returns a parser that consumes the next item in the context.

import { item } from 'parser-lang';

item().tryParse('abc');
// 'a'
item().tryParse('');
// throw Error

satisfy

satisfy(
  f: A => boolean,
  msg?: A => string
): Parser<A>

Returns a parser that consumes the next item from the context and applies the predicate f on the result. The parser fails if the predicate fails and invokes msg with the item result to get the failure message.

import { satisfy } from 'parser-lang';

satisfy(n => n > 2).tryParse([10]);
// 10
satisfy(n => n > 2).tryParse([1, 10]);
// throw Error
satisfy(n => n > 2, n => `${n} is not big enough`).tryParse([1, 10]);
// throw Error('1 is not big enough')

char

char(ch: string): Parser<string>

Returns a parser that matches the character ch.

import { char } from 'parser-lang';

char('a').tryParse('abc');
// 'a'
char('b').tryParse('abc');
// throw Error

string

string(s: string | Iterable): Parser<string>

Returns a parser that matches the string or iterable s.

import { string } from 'parser-lang';

string('foo').tryParse('foobar');
// 'foo'
string('foo').tryParse(['f', 'o', 'o', 'b', 'a', 'r']);
// 'foo'
string('foo').tryParse('bar');
// throw Error

regex

regex(re: RegExp): Parser<string>

Returns a parser that matches the regular expression re.

import { regex } from 'parser-lang';

regex(/foo/).tryParse('foobar');
// 'foo'
regex(/foo/).tryParse('barfoo');
// throw Error

sequence

sequence(
  ...parsers: Parser<A>
): Parser<A[]>

Returns a parser that matches a sequence of parsers and collects their results in an array.

import { sequence } from 'parser-lang';

sequence(char('a'), char('b')).tryParse('abcd');
// ['a', 'b']
sequence(char('a'), char('b')).tryParse('afg');
// throw Error

alternatives

alternatives(
  ...parsers: Parser<A>
): Parser<A>

Returns a parser that tries each parser from parsers and returns the first one that succeeds.

import { alternatives } from 'parser-lang';

alternatives(char('a'), char('b')).tryParse('a');
// 'a'
alternatives(char('a'), char('b')).tryParse('b');
// 'b'
alternatives(char('a'), char('b')).tryParse('c');
// throw Error

Types

Outcome

An Outcome is an abstract class with two implementations, a Success or a Failure. An Outcome is the same as the Either type from haskell and similar languages.

of 

Outcome.of(value: A): Outcome<A>

Returns a Success of value.

map

Outcome<A>#map(f: A => B): Outcome<B>

Return a new outcome with the result of applying f to the value in this outcome.

Outcome.of(1).map(x => x + 1);
// Success { value: 2 }

chain

Outcome<A>#chain(
  f: A => Outcome<B>
): Outcome<B>

Return the result of applying f to the value in this outcome.

forEach

Outcome<A>#forEach(
  f: A => void
): Outcome<A>

Return the original outcome after applying f to the value for its effects.

Context

import { Context } from 'parser-lang`;

The context protocol defines a standard way for mutable iterable objects to be used in an "immutable" way by allowing consumers to make clones before performing mutations.

An object is a context object when:

  • it follows the iterable protocol
  • it has a method accessible on the symbol property [Context.clone] with behavior described below
  • it optionally has a method accessible on the symbol property [Context.regex] with behavior described below

The [Context.clone] method is a zero argument function that must return a fresh clone of the context object. Any subsequent mutations on the original object (e.g. calls to next) must not effect the clone.

The optional [Context.regex] method is a function that takes a single regular expression argument and returns an object with the following properties:

  • done - a boolean indicating if the regular expression matched. The match must start from the current location in the iterator
  • value - the string matched by the regular expression. Only present if done is true

Note the similarities to the next method of an iterator.

ParseResult

type ParseResult<A> = {
  value: A,
  ctx: Context,
};

ParseResult is the type returned from a parse. It represents the value that was parsed along with a new Context the resulted in consuming the previous Context.