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my-simple-either

Simple Type and Function set for Either interface. Either important concept in functional programming. But Node.js and TypeScript not support this concept. So you can choose fp-ts or anther functional utility. But if you need only Eihter, this package is good alternative.

Why? use Either?

Helpful for functional programming and integrate return type. See below.

import { parse as jsoncParse } from 'jsonc-parser';
import { parse as json5Parse } from 'json5';

function json5Parse(value: string): SimpleEither<Error, Record<any, any>> {
  try {
    return pass(json5Parse(value));
  } catch (err) {
    return fail(new Error(err));
  }
}

function jsoncParse(value: string): SimpleEither<Error, Record<any, any>> {
  try {
    return pass(jsoncParse(value));
  } catch (err) {
    return fail(new Error(err));
  }
}

function parse(value: string): Record<any, any> {
  const jsoncParsedEither = jsoncParse(value);

  if (isPass(jsoncParsedEither)) {
    return jsoncParsedEither.pass;
  }

  const json5ParsedEither = json5Parse(value);

  if (isPass(json5ParsedEither)) {
    return json5ParsedEither.pass;    
  }

  // also you can use "throw new Error(jsoncParsedEither.fail);"
  throw new Error(json5ParsedEither.fail);
}

throw keyword move control-flow. But Either, SimpleEither don't move control-flow besides Either helpful functional programming and function pipe.

Either

Name using left and right.

name	description
ILeft	Left interface
IRight	Right interface
Either	Either type using ILeft and IRight
left	value convert ILeft type
right	value convert IRight type
isLeft	check given value is ILeft type
isRight	check given value is IRight type

SimpleEither

Name using pass and fail.

name	description
IFail	Fail interface
IPass	Pass interface
SimpleEither	SimpleEither type using IFail and IPass
fail	value convert IFail type
pass	value convert IPass type
isFail	check given value is IFail type
isPass	check given value is IPass type

Generic type in Either, SimpleEither

First generic type is ILeft or IFail. Because fp-ts and many programming language choose first type is left(or fail).

type Either<TLEFT, TRIGHT> = ILeft<TLEFT> | IRight<TRIGHT>;