About

onia is a lightweight library of monadic parser combinators for JavaScript and TypeScript. It offers a versatile set of functions to create and combine parsers in a modular and composable manner. These parsers are designed to process and interpret structured text, making them ideal for parsing programming languages, data formats, and other text-based protocols.

Installation

$ npm i onia

Usage

Example

import onia, {
    regex,
    alpha,
    map,
    many,
    int,
    sequence,
    optional
} from 'onia';

const digit = map(
    regex(/\d/g, 'digit'),
    int(),
    'digit'
);
const digits = map(
    many(digit),
    (digit) => parseInt(digit.join('')),
    'digits'
);
const whitespace = alpha(' ', 'whitespace');
const optionalWhitespace = optional(whitespace, false);
const operator = regex(/[+-]/g, 'operator');
const expression = map(
    sequence([
        digits,
        optionalWhitespace,
        operator,
        optionalWhitespace,
        digits
    ] as const),
    filter([
        optionalWhitespace
    ]),
    'expression'
);

const result = onia('123 + 321', expression);
// result === [123, '+', 321]

API: Parsers

alpha(char: string, expected?: string): Parser<string>

Creates a parser that matches a specific character.

Parameters:

• char (string): The character to match.
• expected (string, optional): The name of the expected parser.

Returns:

• Parser<string>: A parser that matches the specified character.

Example:

const parser = alpha('a');
const result = parser({index: 0, text: 'abc'});
// result === 'a'

regex(pattern: RegExp, expected?: string): Parser<string>

Creates a parser that matches a regular expression pattern.

Parameters:

• pattern (RegExp): The regular expression pattern to match.
• expected (string, optional): The name of the expected parser.

Returns:

• Parser<string>: A parser that matches the specified pattern.

Example:

const parser = regex(/\d+/);
const result = parser({index: 0, text: '123abc'});
// result === '123'

sequence(parsers: readonly Parser<T>[], expected?: string): Parser<T[]>

Creates a parser that matches a sequence of parsers.

Parameters:

• parsers (readonly Parser[]): The parsers to match in sequence.
• expected (string, optional): The name of the expected parser.

Returns:

• Parser<T[]>: A parser that matches the sequence of input parsers.

Example:

const parser = sequence([alpha('a'), alpha('b'), alpha('c')]);
const result = parser({index: 0, text: 'abc'});
// result === ['a', 'b', 'c']

any(parsers: readonly Parser<T>[], expected?: string): Parser<T>

Creates a parser that matches any one of the provided parsers.

Parameters:

• parsers (readonly Parser[]): The parsers to match.
• expected (string, optional): The name of the expected parser.

Returns:

• Parser<T>: A parser that matches any one of the input parsers.

Example:

const parser = any([alpha('a'), alpha('b')]);
const result = parser({index: 0, text: 'bcd'});
// result === 'b'

optional(parser: Parser<T>, defaultValue?: T, expected?: string): Parser<T | undefined>

Creates a parser that optionally matches another parser.

Parameters:

• parser (Parser): The parser to optionally match.
• defaultValue (T, optional): The default value if the parser does not match.
• expected (string, optional): The name of the expected parser.

Returns:

• Parser<T | undefined>: A parser that optionally matches the input parser.

Example:

const parser = optional(alpha('a'));
const result = parser({index: 0, text: 'bcd'});
// result === undefined

many(parser: Parser<T>, expected?: string): Parser<T[]>

Creates a parser that matches zero or more occurrences of another parser.

Parameters:

• parser (Parser): The parser to match multiple times.
• expected (string, optional): The name of the expected parser.

Returns:

• Parser<T[]>: A parser that matches zero or more occurrences of the input parser.

Example:

const parser = many(alpha('a'));
const result = parser({index: 0, text: 'aaabc'});
// result === ['a', 'a', 'a']

map(parser: Parser<T>, transform: (value: T) => U, expected?: string): Parser<U>

Creates a parser that transforms the result of another parser.

Parameters:

• parser (Parser): The parser to transform.
• transform (function): The transformation function.
• expected (string, optional): The name of the expected parser.

Returns:

• Parser<U>: A parser that transforms the result of the input parser.

Example:

const parser = map(alpha('a'), (char) => char.toUpperCase());
const result = parser({index: 0, text: 'abc'});
// result === 'A'

lazy<T>(parserFactory: () => Parser<T>, expected?: string): Parser<T>

Creates a parser that is lazily evaluated.

Parameters:

• parserFactory (function): A function that returns the parser to be evaluated.
• expected (string, optional): The name of the expected parser.

Returns:

• Parser<T>: A lazily evaluated parser.

Example:

const parser = lazy(() => alpha('a'));
const result = parser({index: 0, text: 'abc'});
// result === 'a'

API: Helpers

flatten(): (haystack: T) => FlattenArray<T>

Flattens a nested array by one level.

Example:

const flattenArray = flatten();
const result = flattenArray([['a', 'b'], ['c', 'd']]);
// result === ['a', 'b', 'c', 'd']

pop(): (haystack: T) => LastElement<T>

Returns the last element of an array.

Example:

const popElement = pop();
const result = popElement(['a', 'b', 'c']);
// result === 'c'

shift(): (haystack: T) => FirstElement<T>

Returns the first element of an array.

Example:

const shiftElement = shift();
const result = shiftElement(['a', 'b', 'c']);
// result === 'a'

join(): (haystack: T) => string

Joins all elements of an array into a string.

Example:

const joinElements = join();
const result = joinElements(['a', 'b', 'c']);
// result === 'abc'

expand(): <T>(...haystack: T) => ReadonlyArray<T>

Expands the elements of an array.

Example:

const expandElements = expand();
const result = expandElements(1, 2, 3);
// result === [1, 2, 3]

zip(mapper: (parser: Parser<V>, value: T) => R): (values: ReadonlyArray<T>) => ReadonlyArray<R>

Maps each element of an array using a provided function.

Example:

const stringParser = alpha('foo');
const numberParser = map(regex(/\d/g), int());

const zipParser = map(
    sequence([numberParser, stringParser, numberParser] as const),
    zip((parser, value) => {
        if (parser === stringParser) {
            value = '2';
        }
        return value;
    })
);

const result = zipParser({index: 0, text: '1foo3'});
// result === [1, '2', 3]

int(): (number: string) => number

Parses a string as an integer.

Example:

const parseInt = int();
const result = parseInt('123');
// result === 123

float(): (number: string) => number

Parses a string as a float.

Example:

const parseFloat = float();
const result = parseFloat('123.45');
// result === 123.45

filter(values: T, strict: boolean = false): (haystack: H) => H

Filters out specified values from an array.

Parameters:

• values (T): Values to filter out.
• strict (boolean, optional): Filter falsy values out.

Example:

const filterValues = filter([alpha('a'), 'b']);
const result = filterValues(['a', 'b', null, 'c', 'd'] as const, true);
// result === ['c', 'd']

pipe(...fns: Function[]): Function

Composes multiple functions into a single function.

Example:

const pipeline = pipe(
    (number: number) => number + 1,
    (number: number) => number * 2,
    (number: number) => number.toString(),
    join()
);
const result = pipeline([1, 2, 3]);
// result === '468'

Disclaimer

This project is still in early development and is subject to change.

Licence

MIT License, see LICENSE