API / Belt / Belt_Result

Belt_Result

Result types are really useful to describe the result of a certain operation without relying on exceptions or option types.

This module gives you useful utilities to create and combine Result data.

t

type t<'a, 'b> = Ok('a) | Error('b)

getExn

getExn(res): when res is Ok(n), returns n when res is Error(m), raise an exception

RES
Belt.Result.getExn(Belt.Result.Ok(42)) == 42

Belt.Result.getExn(Belt.Result.Error("Invalid data")) /* raises exception */

let getExn: t<'a, 'b> => 'a

mapWithDefaultU

let mapWithDefaultU: (t<'a, 'c>, 'b, (. 'a) => 'b) => 'b

mapWithDefault

mapWithDefault(res, default, f): When res is Ok(n), returns f(n), otherwise default.

RES
let ok = Belt.Result.Ok(42)
Belt.Result.mapWithDefault(ok, 0, (x) => x / 2) == 21

let error = Belt.Result.Error("Invalid data")
Belt.Result.mapWithDefault(error, 0, (x) => x / 2) == 0

let mapWithDefault: (t<'a, 'c>, 'b, 'a => 'b) => 'b

mapU

let mapU: (t<'a, 'c>, (. 'a) => 'b) => t<'b, 'c>

map

map(res, f): When res is Ok(n), returns Ok(f(n)). Otherwise returns res unchanged. Function f takes a value of the same type as n and returns an ordinary value.

RES
let f = (x) => sqrt(Belt.Int.toFloat(x))

Belt.Result.map(Ok(64), f) == Ok(8.0)

Belt.Result.map(Error("Invalid data"), f) == Error("Invalid data")

let map: (t<'a, 'c>, 'a => 'b) => t<'b, 'c>

flatMapU

let flatMapU: (t<'a, 'c>, (. 'a) => t<'b, 'c>) => t<'b, 'c>

flatMap

flatMap(res, f): When res is Ok(n), returns f(n). Otherwise, returns res unchanged. Function f takes a value of the same type as n and returns a Belt.Result.

RES
let recip = (x) =>
  if (x !== 0.0) {
    Belt.Result.Ok(1.0 /. x)
  } else {
    Belt.Result.Error("Divide by zero")
  }

Belt.Result.flatMap(Ok(2.0), recip) == Ok(0.5)

Belt.Result.flatMap(Ok(0.0), recip) == Error("Divide by zero")

Belt.Result.flatMap(Error("Already bad"), recip) == Error("Already bad")

let flatMap: (t<'a, 'c>, 'a => t<'b, 'c>) => t<'b, 'c>

getWithDefault

getWithDefault(res, defaultValue): If res is Ok(n), returns n, otherwise default

RES
Belt.Result.getWithDefault(Ok(42), 0) == 42

Belt.Result.getWithDefault(Error("Invalid Data"), 0) == 0

let getWithDefault: (t<'a, 'b>, 'a) => 'a

isOk

isOk(res): Returns true if res is of the form Ok(n), false if it is the Error(e) variant.

let isOk: t<'a, 'b> => bool

isError

isError(res): Returns true if res is of the form Error(e), false if it is the Ok(n) variant.

let isError: t<'a, 'b> => bool

eqU

let eqU: (t<'a, 'c>, t<'b, 'd>, (. 'a, 'b) => bool) => bool

eq

eq(res1, res2, f): Determine if two Belt.Result variables are equal with respect to an equality function. If res1 and res2 are of the form Ok(n) and Ok(m), return the result of f(n, m). If one of res1 and res2 are of the form Error(e), return false If both res1 and res2 are of the form Error(e), return true

RES
let good1 = Belt.Result.Ok(42)

let good2 = Belt.Result.Ok(32)

let bad1 = Belt.Result.Error("invalid")

let bad2 = Belt.Result.Error("really invalid")

let mod10equal = (a, b) => mod(a, 10) === mod(b, 10)

Belt.Result.eq(good1, good2, mod10equal) == true

Belt.Result.eq(good1, bad1, mod10equal) == false

Belt.Result.eq(bad2, good2, mod10equal) == false

Belt.Result.eq(bad1, bad2, mod10equal) == true

let eq: (t<'a, 'c>, t<'b, 'd>, ('a, 'b) => bool) => bool

cmpU

let cmpU: (t<'a, 'c>, t<'b, 'd>, (. 'a, 'b) => int) => int

cmp

cmp(res1, res2, f): Compare two Belt.Result variables with respect to a comparison function. The comparison function returns -1 if the first variable is "less than" the second, 0 if the two variables are equal, and 1 if the first is "greater than" the second.

If res1 and res2 are of the form Ok(n) and Ok(m), return the result of f(n, m). If res1 is of the form Error(e) and res2 of the form Ok(n), return -1 (nothing is less than something) If res1 is of the form Ok(n) and res2 of the form Error(e), return 1 (something is greater than nothing) If both res1 and res2 are of the form Error(e), return 0 (equal)

RES
let good1 = Belt.Result.Ok(59)

let good2 = Belt.Result.Ok(37)

let bad1 = Belt.Result.Error("invalid")

let bad2 = Belt.Result.Error("really invalid")

let mod10cmp = (a, b) => Pervasives.compare(mod(a, 10), mod(b, 10))

Belt.Result.cmp(Ok(39), Ok(57), mod10cmp) == 1

Belt.Result.cmp(Ok(57), Ok(39), mod10cmp) == (-1)

Belt.Result.cmp(Ok(39), Error("y"), mod10cmp) == 1

Belt.Result.cmp(Error("x"), Ok(57), mod10cmp) == (-1)

Belt.Result.cmp(Error("x"), Error("y"), mod10cmp) == 0

let cmp: (t<'a, 'c>, t<'b, 'd>, ('a, 'b) => int) => int