Result

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.

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import Result from "result"

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

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

Values

Functions for working with the Result data type.

Result.isOk

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isOk : Result<a, b> -> Bool

Checks if the Result is the Ok variant.

Parameters:

Returns:

Result.isErr

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isErr : Result<a, b> -> Bool

Checks if the Result is the Err variant.

Parameters:

Returns:

Result.toOption

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toOption : Result<a, b> -> Option<a>

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

Parameters:

Returns:

Result.flatMap

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flatMap : ((a -> Result<b, c>), 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:

Returns:

Result.flatMapErr

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flatMapErr : ((a -> Result<b, c>), 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:

Returns:

Result.map

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map : ((a -> b), 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:

Returns:

Result.mapErr

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mapErr : ((a -> b), 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:

Returns:

Result.mapWithDefault

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mapWithDefault : ((a -> b), b, 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:

Returns:

Result.mapWithDefaultFn

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mapWithDefaultFn : ((a -> b), (c -> b), 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:

Returns:

Result.or

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or : (Result<a, b>, 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:

Returns:

Result.and

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and : (Result<a, b>, 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:

Returns:

Result.peek

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peek : ((a -> b), (c -> d), 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:

Result.peekOk

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peekOk : ((a -> b), Result<a, c>) -> Void

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

Parameters:

Result.peekErr

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peekErr : ((a -> b), Result<c, a>) -> Void

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

Parameters:

Result.expect

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expect : (String, Result<a, b>) -> a

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

Parameters:

Returns:

Throws:

Failure(String)

• When the result is Err

Examples:

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

Result.unwrap

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unwrap : 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:

Returns:

Throws:

Failure(String)

• When the result is Err

Examples:

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