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import { flow, identity, pipe } from 'fp-ts/function'
import { Either, left, right, map, chain, mapLeft, fold, orElse } from 'fp-ts/Either'
type char = string
type ParserResult<T> = [T, string]
type ParserError = [string, string]
type Parser<T> = (input: string) => Either<ParserError, ParserResult<T>>
export const many0 = <T>(parser: Parser<T>): Parser<Array<T>> => flow(
parser,
chain(([a, nextInput]) =>
pipe(
nextInput,
many0(parser),
map(([ls, inp]): ParserResult<T[]> => [[a, ...ls], inp]),
)
),
orElse(([_, inp]) => right([[] as T[], inp]))
)
export const many1 = <T>(parser: Parser<T>): Parser<Array<T>> => flow(
many0(parser),
chain(([res, inp]) =>
res.length > 0 ? right([res, inp]) : left([`many1 failed to parse at ${inp}`, inp]))
)
export const satify_char = (f: (c: char) => boolean): Parser<char> => (input: string) => {
const c = input.charAt(0)
if (f(c)) return right([c, input.slice(1)])
return left([`Expected to satisfy ${f}, got "${c}"`, input])
};
export const digit = satify_char(c => /^[0-9]$/g.test(c))
export const integer: Parser<number> = flow(
many1(digit),
map(([ds, input]) => [parseInt(ds.join(''), 10), input])
)
export const or = <T>(parsers: Parser<T>[]): Parser<T> => {
const ppp = ([p, ...ps]: Parser<T>[]) => flow(
p,
orElse(([_, inp]) => or(ps)(inp))
)
return parsers.length > 0 ? ppp(parsers) : (inp: string) => left(['unable to match', inp])
}
export const space = satify_char(c => c === ' ')
export const newline = satify_char(c => c === '\n')
export const tab = satify_char(c => c === '\t')
export const whitespace = or([space, newline, tab])
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