ResultModule

PackageReified.Result

Fail-fast helpers over the standard F# Result type.

Summary

Name	Signature	Synopsis
Operations
ok	ok value	Creates an Ok result.
error	error failure	Creates an Error result.
map	map mapper result	Maps the success value of a result.
mapError	mapError mapper result	Maps the error value of a result.
bind	bind binder result	Binds a result to the next fail-fast operation.
orElseWith	orElseWith fallback result	Computes a fallback result from the source error when the result fails.
orElse	orElse fallback result	Falls back to another result when the source result fails.
okIf	okIf predicate input	Keeps the input value when the predicate holds, or returns the supplied error.
failIf	failIf predicate input	Keeps the input value when the predicate does not hold, or returns the supplied error.
require	require condition	Requires an already-computed condition where there is no subject value to preserve.
orError	orError failure result	Replaces whatever error a result carries with the supplied typed error.
fromTry	fromTry (tryResult, tryResult)	Converts a .NET Try* tuple into a unit-error result.
fromChoice	fromChoice choice	Converts an F# Choice into a result.
fromOption	fromOption value	Converts an option into a unit-error result.
fromValueOption	fromValueOption value	Converts a value option into a unit-error result.
toOption	toOption result	Drops the error channel and returns Some for success.
toValueOption	toValueOption result	Drops the error channel and returns ValueSome for success.
defaultValue	defaultValue fallback result	Returns the success value or the supplied fallback value.
tap	tap effect result	Runs a side effect on the successful value and returns the result unchanged.
tapError	tapError effect result	Runs a side effect on the error value and returns the result unchanged.
traverse	traverse mapping values	Maps each value with a result-returning function, stopping at the first error.
sequence	sequence values	Turns a sequence of results into one fail-fast result containing all successes.
traverseAll	traverseAll mapping values	Maps each value with a result-returning function, running every mapping and collecting every error.
sequenceAll	sequenceAll values	Turns a sequence of results into one result containing all successes, or every error.

Operations

kind:member

ok

ok value

Member

Creates an Ok result.

Parameters

Name	Type	Description
value	'a

Returns

Result<'a, 'b>

kind:member

error

error failure

Member

Creates an Error result.

Parameters

Name	Type	Description
failure	'a

Returns

Result<'b, 'a>

kind:member

map

map mapper result

Member

Maps the success value of a result.

Parameters

Name	Type	Description
mapper	'a -> 'b
result	Result<'a, 'c>

Returns

Result<'b, 'c>

kind:member

mapError

mapError mapper result

Member

Maps the error value of a result.

Parameters

Name	Type	Description
mapper	'a -> 'b
result	Result<'c, 'a>

Returns

Result<'c, 'b>

kind:member

bind

bind binder result

Member

Binds a result to the next fail-fast operation.

Parameters

Name	Type	Description
binder	'a -> Result<'b, 'c>
result	Result<'a, 'c>

Returns

Result<'b, 'c>

kind:member

orElseWith

orElseWith fallback result

Member

Computes a fallback result from the source error when the result fails.

Parameters

Name	Type	Description
fallback	'error -> Result<'value, 'error>
result	Result<'value, 'error>

Returns

Result<'value, 'error>

Verification Examples

let result = Error "boom"
result |> Result.orElseWith (fun error -> Ok (String.length error)) // Ok 4

kind:member

orElse

orElse fallback result

Member

Falls back to another result when the source result fails.

Parameters

Name	Type	Description
fallback	Result<'value, 'error>
result	Result<'value, 'error>

Returns

Result<'value, 'error>

Verification Examples

let result = Error "boom"
result |> Result.orElse (Ok 5) // Ok 5

kind:member

okIf

okIf predicate input

Member

Keeps the input value when the predicate holds, or returns the supplied error.

Parameters

Name	Type	Description
predicate	'input -> bool
input	'input

Returns

Result<'input, unit>

kind:member

failIf

failIf predicate input

Member

Keeps the input value when the predicate does not hold, or returns the supplied error.

Parameters

Name	Type	Description
predicate	'input -> bool
input	'input

Returns

Result<'input, unit>

kind:member

require

require condition

Member

Requires an already-computed condition where there is no subject value to preserve.

Parameters

Name	Type	Description
condition	bool

Returns

Result<unit, unit>

Verification Examples

request.AcceptedTerms |> Result.require |> Result.orError TermsNotAccepted

kind:member

orError

orError failure result

Member

Replaces whatever error a result carries with the supplied typed error. Ok passes through unchanged.

Parameters

Name	Type	Description
failure	'error
result	Result<'value, 'discardedError>

Returns

Result<'value, 'error>

kind:member

fromTry

fromTry (tryResult, tryResult)

Member

Converts a .NET Try* tuple into a unit-error result.

Parameters

Name	Type	Description
tryResult	bool
tryResult	'value

Returns

Result<'value, unit>

kind:member

fromChoice

fromChoice choice

Member

Converts an F# Choice into a result.

Parameters

Name	Type	Description
choice	Choice<'value, 'error>

Returns

Result<'value, 'error>

kind:member

fromOption

fromOption value

Member

Converts an option into a unit-error result. The inverse of toOption.

Parameters

Name	Type	Description
value	'value option

Returns

Result<'value, unit>

kind:member

fromValueOption

fromValueOption value

Member

Converts a value option into a unit-error result. The inverse of toValueOption.

Parameters

Name	Type	Description
value	'value voption

Returns

Result<'value, unit>

kind:member

toOption

toOption result

Member

Drops the error channel and returns Some for success.

Parameters

Name	Type	Description
result	Result<'value, 'error>

Returns

'value option

kind:member

toValueOption

toValueOption result

Member

Drops the error channel and returns ValueSome for success.

Parameters

Name	Type	Description
result	Result<'value, 'error>

Returns

'value voption

kind:member

defaultValue

defaultValue fallback result

Member

Returns the success value or the supplied fallback value.

Parameters

Name	Type	Description
fallback	'value
result	Result<'value, 'error>

Returns

'value

kind:member

tap

tap effect result

Member

Runs a side effect on the successful value and returns the result unchanged.

Parameters

Name	Type	Description
effect	'value -> unit
result	Result<'value, 'error>

Returns

Result<'value, 'error>

Verification Examples

Ok 10 |> Result.tap (printfn "loaded %d") // prints, then returns Ok 10

kind:member

tapError

tapError effect result

Member

Runs a side effect on the error value and returns the result unchanged.

Parameters

Name	Type	Description
effect	'error -> unit
result	Result<'value, 'error>

Returns

Result<'value, 'error>

Verification Examples

Error "boom" |> Result.tapError (printfn "failed: %s") // prints, then returns Error "boom"

kind:member

traverse

traverse mapping values

Member

Maps each value with a result-returning function, stopping at the first error.

Parameters

Name	Type	Description
mapping	'input -> Result<'output, 'error>
values	'input seq

Returns

Result<'output list, 'error>

Verification Examples

[ "1"; "2" ] |> Result.traverse parseInt // Ok [ 1; 2 ]

kind:member

sequence

sequence values

Member

Turns a sequence of results into one fail-fast result containing all successes.

Parameters

Name	Type	Description
values	Result<'value, 'error> seq

Returns

Result<'value list, 'error>

Verification Examples

[ Ok 1; Error "missing"; Ok 3 ] |> Result.sequence // Error "missing"

kind:member

traverseAll

traverseAll mapping values

Member

Maps each value with a result-returning function, running every mapping and collecting every error.

Parameters

Name	Type	Description
mapping	'input -> Result<'output, 'error>
values	'input seq

Returns

Result<'output list, 'error list>

Verification Examples

[ "1"; "x"; "y" ] |> Result.traverseAll parseInt // Error [ NotANumber "x"; NotANumber "y" ]

kind:member

sequenceAll

sequenceAll values

Member

Turns a sequence of results into one result containing all successes, or every error.

Parameters

Name	Type	Description
values	Result<'value, 'error> seq

Returns

Result<'value list, 'error list>

Verification Examples

[ Ok 1; Error "missing"; Error "invalid" ] |> Result.sequenceAll // Error [ "missing"; "invalid" ]