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Utilities for working with the Result data type.

The Result type is an enum that represents the possibility of a success case (with the Ok variant), or an error case (with the Err variant). Use a Result as the return type of a function that may return an error.

Added in 0.2.0

No other changes yet.

from "result" include Result

let success = Ok((x) => 1 + x) // Creates a successful Result containing (x) => 1 + x

let failure = Err("Something bad happened") // Creates an unsuccessful Result containing "Something bad happened"

Values

Functions and constants included in the Result module.

Result.isOk

Added in 0.2.0

No other changes yet.

isOk : (result: Result<a, b>) => Bool

Checks if the Result is the Ok variant.

Parameters:

param	type	description
`result`	`Result<a, b>`	The result to check

result: The result to check

Returns:

type	description
`Bool`	`true` if the Result is the `Ok` variant or `false` otherwise

Bool: true if the Result is the Ok variant or false otherwise

Result.isErr

Added in 0.2.0

No other changes yet.

isErr : (result: Result<a, b>) => Bool

Checks if the Result is the Err variant.

Parameters:

param	type	description
`result`	`Result<a, b>`	The result to check

result: The result to check

Returns:

type	description
`Bool`	`true` if the Result is the `Err` variant or `false` otherwise

Bool: true if the Result is the Err variant or false otherwise

Result.toOption

Added in 0.2.0

No other changes yet.

toOption : (result: Result<a, b>) => Option<a>

Converts the Result to an Option. An error value is discarded and replaced with None.

Parameters:

param	type	description
`result`	`Result<a, b>`	The result to convert

result: The result to convert

Returns:

type	description
`Option<a>`	`Some(value)` if the Result is `Ok(value)` or `None` if the Result is an `Err`

Option<a>: Some(value) if the Result is Ok(value) or None if the Result is an Err

Result.flatMap

Added in 0.2.0

No other changes yet.

flatMap : (fn: (a => Result<b, c>), result: Result<a, c>) => Result<b, c>

If the Result is Ok(value), applies the given function to the value to produce a new Result.

Parameters:

param	type	description
`fn`	`a => Result<b, c>`	The function to call on the value of an `Ok` variant
`result`	`Result<a, c>`	The result to map

fn: The function to call on the value of an Ok variant

result: The result to map

Returns:

type	description
`Result<b, c>`	A new Result produced by the mapping function if the variant was `Ok` or the unmodified `Err` otherwise

Result<b, c>: A new Result produced by the mapping function if the variant was Ok or the unmodified Err otherwise

Result.flatMapErr

Added in 0.2.0

No other changes yet.

flatMapErr : (fn: (a => Result<b, c>), result: Result<b, a>) => Result<b, c>

If the Result is an Err(value), applies the given function to the value to produce a new Result.

Parameters:

param	type	description
`fn`	`a => Result<b, c>`	The function to call on the value of an `Err` variant
`result`	`Result<b, a>`	The result to map

fn: The function to call on the value of an Err variant

result: The result to map

Returns:

type	description
`Result<b, c>`	A new Result produced by the mapping function if the variant was `Err` or the unmodified `Ok` otherwise

Result<b, c>: A new Result produced by the mapping function if the variant was Err or the unmodified Ok otherwise

Result.map

Added in 0.2.0

No other changes yet.

map : (fn: (a => b), result: Result<a, c>) => Result<b, c>

If the Result is Ok(value), applies the given function to the value and wraps the new value in an Ok variant.

Parameters:

param	type	description
`fn`	`a => b`	The function to call on the value of an `Ok` variant
`result`	`Result<a, c>`	The result to map

fn: The function to call on the value of an Ok variant

result: The result to map

Returns:

type	description
`Result<b, c>`	A new `Ok` variant produced by the mapping function if the variant was `Ok` or the unmodified `Err` otherwise

Result<b, c>: A new Ok variant produced by the mapping function if the variant was Ok or the unmodified Err otherwise

Result.mapErr

Added in 0.2.0

No other changes yet.

mapErr : (fn: (a => b), result: Result<c, a>) => Result<c, b>

If the Result is Err(value), applies the given function to the value and wraps the new value in an Err variant.

Parameters:

param	type	description
`fn`	`a => b`	The function to call on the value of an `Err` variant
`result`	`Result<c, a>`	The result to map

fn: The function to call on the value of an Err variant

result: The result to map

Returns:

type	description
`Result<c, b>`	A new `Err` variant produced by the mapping function if the variant was `Err` or the unmodified `Ok` otherwise

Result<c, b>: A new Err variant produced by the mapping function if the variant was Err or the unmodified Ok otherwise

Result.mapWithDefault

Added in 0.2.0

No other changes yet.

mapWithDefault : (fn: (a => b), def: b, result: Result<a, c>) => b

If the Result is Ok(value), applies the given function to the value to produce a new value, otherwise uses the default value. Useful for unwrapping a successful Result while providing a fallback for any errors that can occur.

Parameters:

param	type	description
`fn`	`a => b`	The function to call on the value of an `Ok` variant
`def`	`b`	A fallback value for an `Err` variant
`result`	`Result<a, c>`	The result to map

fn: The function to call on the value of an Ok variant

def: A fallback value for an Err variant

result: The result to map

Returns:

type	description
`b`	The value produced by the mapping function if the result is of the `Ok` variant or the default value otherwise

b: The value produced by the mapping function if the result is of the Ok variant or the default value otherwise

Result.mapWithDefaultFn

Added in 0.2.0

No other changes yet.

mapWithDefaultFn :
  (fnOk: (a => b), fnErr: (c => b), result: Result<a, c>) => b

If the Result is Ok(value), applies the fnOk function to the value to produce a new value. If the Result is Err(value), applies the fnErr function to the value to produce a new value. Useful for unwrapping a Result into a value, whether it is successful or unsuccessful.

Parameters:

param	type	description
`fnOk`	`a => b`	The function to call on the value of an `Ok` variant
`fnErr`	`c => b`	The function to call on the value of an `Err` variant
`result`	`Result<a, c>`	The result to map

fnOk: The function to call on the value of an Ok variant

fnErr: The function to call on the value of an Err variant

result: The result to map

Returns:

type	description
`b`	The value produced by one of the mapping functions

b: The value produced by one of the mapping functions

Result.(||)

Added in 0.6.0

version	changes
`0.2.0`	Originally named `or`

(||) : (result1: Result<a, b>, result2: Result<a, b>) => Result<a, b>

Behaves like a logical OR (||) where the first Result is only returned if it is the Ok variant and falling back to the second Result in all other cases.

Parameters:

param	type	description
`result1`	`Result<a, b>`	The first result
`result2`	`Result<a, b>`	The second result

result1: The first result

result2: The second result

Returns:

type	description
`Result<a, b>`	The first Result if it is the `Ok` variant or the second Result otherwise

Result<a, b>: The first Result if it is the Ok variant or the second Result otherwise

Result.(&&)

Added in 0.6.0

version	changes
`0.2.0`	Originally named `and`

(&&) : (result1: Result<a, b>, result2: Result<a, b>) => Result<a, b>

Behaves like a logical AND (&&) where the first Result is only returned if it is the Err variant and falling back to the second Result in all other cases.

Parameters:

param	type	description
`result1`	`Result<a, b>`	The first result
`result2`	`Result<a, b>`	The second result

result1: The first result

result2: The second result

Returns:

type	description
`Result<a, b>`	The second Result if both are the `Ok` variant or the first Result otherwise

Result<a, b>: The second Result if both are the Ok variant or the first Result otherwise

Result.peek

Added in 0.2.0

No other changes yet.

peek : (fnOk: (a => b), fnErr: (c => d), result: Result<a, c>) => Void

If the Result is Ok(value), applies the fnOk function to the value without producing a new value. If the Result is Err(value), applies the fnErr function to the value without producing a new value. Useful for inspecting Results without changing anything.

Parameters:

param	type	description
`fnOk`	`a => b`	The function to call on the value of an `Ok` variant
`fnErr`	`c => d`	The function to call on the value of an `Err` variant
`result`	`Result<a, c>`	The result to inspect

fnOk: The function to call on the value of an Ok variant

fnErr: The function to call on the value of an Err variant

result: The result to inspect

Result.peekOk

Added in 0.2.0

No other changes yet.

peekOk : (fn: (a => b), result: Result<a, c>) => Void

If the Result is Ok(value), applies the given function to the value without producing a new value.

Parameters:

param	type	description
`fn`	`a => b`	The function to call on the value of an `Ok` variant
`result`	`Result<a, c>`	The result to inspect

fn: The function to call on the value of an Ok variant

result: The result to inspect

Result.peekErr

Added in 0.2.0

No other changes yet.

peekErr : (fn: (a => b), result: Result<c, a>) => Void

If the Result is Err(value), applies the given function to the value without producing a new value.

Parameters:

param	type	description
`fn`	`a => b`	The function to call on the value of an `Err` variant
`result`	`Result<c, a>`	The result to inspect

fn: The function to call on the value of an Err variant

result: The result to inspect

Result.expect

Added in 0.4.0

No other changes yet.

expect : (msg: String, result: Result<a, b>) => a

Extracts the value inside an Ok result, otherwise throw an exception containing the message and contents of the Err.

Parameters:

param	type	description
`msg`	`String`	The message to prepend if the result contains an `Err`
`result`	`Result<a, b>`	The result to extract a value from

msg: The message to prepend if the result contains an Err

result: The result to extract a value from

Returns:

type	description
`a`	The unwrapped value if the Result is the `Ok` variant

a: The unwrapped value if the Result is the Ok variant

Throws:

Failure(String)

When the result is Err

Examples:

Result.expect("Unexpected error", Ok(1234)) + 42

Result.unwrap

Added in 0.4.0

No other changes yet.

unwrap : (result: Result<a, b>) => a

Extracts the value inside an Ok result, otherwise throw an exception containing a default message and contents of the Err.

Parameters:

param	type	description
`result`	`Result<a, b>`	The result to extract a value from

result: The result to extract a value from

Returns:

type	description
`a`	The unwrapped value if the result is the `Ok` variant

a: The unwrapped value if the result is the Ok variant

Throws:

Failure(String)

When the result is Err

Examples:

Result.unwrap(Err("This will throw"))

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The Guide

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Standard Library

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The Guide

Reference

Standard Library

Result

Values

Result.isOk

Result.isErr

Result.toOption

Result.flatMap

Result.flatMapErr

Result.map

Result.mapErr

Result.mapWithDefault

Result.mapWithDefaultFn

Result.(||)

Result.(&&)

Result.peek

Result.peekOk

Result.peekErr

Result.expect

Result.unwrap