rust-result.js

Mimic Rust's std::result.

Installation

npm install rust-result

Usage

var fs = require('fs');
var Result = require('./');


// If you want async just get a promise or something.
var readFile = function (path, encoding) {
  try {
    return Result.Ok(fs.readFileSync(path, encoding))
  }
  catch (ex) {
    return Result.Err(ex)
  }
}

var result = readFile(__filename);
var v, err;

if (Result.isOk(result)) {
  v = Result.Ok(result);
  console.log('got ' + v.length + ' bytes')
}
else if (Result.isErr(result)) {
  err = Result.Err(result);
  console.error('oops!', err.message)
}

result = readFile(__filename + 'I do not exist')
if (Result.isOk(result)) {
  v = Result.Ok(result)
  console.log('got ' + v.length + ' bytes')
}
else if (Result.isErr(result)) {
  err = Result.Err(result)
  console.error('oops!', err.message)
}

Documentation

type OkResult<T> : {
  v: T
}
type ErrResult<E <: Error> : {
  err: E
}

rust-result : {
  Ok: ((T) => OkResult<T>) |
    ((OkResult<T>) => T) |
    ((ErrResult<E>) => void),
  isOk: ((OkResult<T>) => true) |
    ((ErrResult<E>) => false)
  Err: ((E <: Error) => ErrResult<E>) |
    ((ErrResult<E>) => E) |
    ((OkResult<T>) => void),
  isErr: ((ErrResult<E>) => true) |
    ((OkResult<T>) => false)
}

Result.Ok

The Result.Ok function is overloaded to do one of two things. It can create a new Ok instance or it can check whether the argument is an instance of Ok

If you call Result.Ok with a plain value it will return an instance of Ok that boxes your plain value.

If you call Result.Ok with either an Err or an Ok instance then it will return undefined for the Err and return the value boxed in the Ok

Result.isOk

The Result.isOk function just checks whether the argument is an instance of Ok.

This predicate function returns true if you pass it an Ok and returns false if you pass it an Err

Result.Err

The Result.Err function is overloaded to do one of two things. It can create a new Err instance or it can check whether the argument is an instance of Err

If you call Result.Err with a plain error it will return an instance of Err that boxes your plain error.

If you call Result.Err with either an Err or an Ok instance then it will return undefined for the Ok and return the value err in the Err

Result.isErr

The Result.isErr function just checks whether the argument is an instance of Err.

This predicate function returns true if you pass it an Err and returns false if you pass it an Ok

MIT Licenced.