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.

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

Examples

RESCRIPT
let ok = Ok(42)
Result.mapOr(ok, 0, (x) => x / 2) == 21

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

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.

Examples

RESCRIPT
let f = (x) => sqrt(Int.toFloat(x))

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

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

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 Result.

Examples

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

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

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

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

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

Examples

RESCRIPT
Result.getOr(Ok(42), 0) == 42

Result.getOr(Error("Invalid Data"), 0) == 0

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

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

equal(res1, res2, f): Determine if two 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

Examples

RESCRIPT
let good1 = Ok(42)

let good2 = Ok(32)

let bad1 = Error("invalid")

let bad2 = Error("really invalid")

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

Result.equal(good1, good2, mod10equal) == true

Result.equal(good1, bad1, mod10equal) == false

Result.equal(bad2, good2, mod10equal) == false

Result.equal(bad1, bad2, mod10equal) == true

compare(res1, res2, f): Compare two 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)

Examples

RESCRIPT
let good1 = Ok(59)

let good2 = Ok(37)

let bad1 = Error("invalid")

let bad2 = Error("really invalid")

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

Result.compare(Ok(39), Ok(57), mod10cmp) == 1.

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

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

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

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

forEach(res, f) runs the provided function f on the Ok value. If res is Error, nothing happens.

Examples

RESCRIPT
Result.forEach(Ok(3), Console.log) // Logs "3", returns ()
Result.forEach(Error("x"), Console.log) // Does nothing, returns ()

mapError(r, f) generates a new result by applying the function f to the Error value. If the source is Ok, return it as-is.

Examples

RESCRIPT
let format = n => `Error code: ${n->Int.toString}`
Result.mapError(Error(14), format) // Error("Error code: 14")
Result.mapError(Ok("abc"), format) // Ok("abc")