Validation on FsFlow

FsFlow.ValidationModule.apply

Mon, 01 Jan 0001 00:00:00 +0000

Applies a validation-wrapped function to a validation-wrapped value.

Parameters

validation: The validation containing the function.
value: The validation containing the value.

Returns

The result of applying the function to the value, with accumulated errors.

FsFlow.ValidationModule.at

Mon, 01 Jan 0001 00:00:00 +0000

Scopes a validation under the supplied path segments.

Parameters

path: The path segments to apply to the validation.
validation: The validation to scope.

Returns

A validation nested under the given path.

FsFlow.ValidationModule.bind

Mon, 01 Jan 0001 00:00:00 +0000

Sequences a validation-producing continuation.

Remarks

This is the monadic “bind” for validation. Note that this operation short-circuits and does not accumulate errors from the binder if the source has already failed. For accumulation, use map2 or the applicative and! syntax.

Parameters

binder: A function of type 'value -> Validation<'next, 'error>.
validation: The source validation.

Returns

The result of the binder or the original diagnostics.

FsFlow.ValidationModule.collect

Mon, 01 Jan 0001 00:00:00 +0000

Collects a sequence of validations into a single validation of a list.

Remarks

This operation is applicative: it will collect errors from ALL items in the sequence.

Parameters

validations: A sequence of type seq<Validation<'value, 'error>>.

Returns

A validation containing the list of values or accumulated diagnostics.

FsFlow.ValidationModule.error

Mon, 01 Jan 0001 00:00:00 +0000

Creates a failing validation result with the provided diagnostics.

Parameters

diagnostics: The Diagnostics graph.

Returns

A failing Validation.

FsFlow.ValidationModule.fail

Mon, 01 Jan 0001 00:00:00 +0000

Alias for error.

Parameters

diagnostics: The Diagnostics graph.

Returns

A failing Validation.

FsFlow.ValidationModule.fromResult

Mon, 01 Jan 0001 00:00:00 +0000

Lifts a standard Result into the Validation context.

Remarks

If the result is an error, it is wrapped in a root-level Diagnostics graph.

Parameters

result: The result to lift.

Returns

A Validation mirroring the result.

FsFlow.ValidationModule.ignore

Mon, 01 Jan 0001 00:00:00 +0000

Maps a successful validation value to unit while preserving the diagnostics.

Parameters

validation: The source validation.

Returns

A validation that keeps the original diagnostics and discards the success value.

FsFlow.ValidationModule.index

Mon, 01 Jan 0001 00:00:00 +0000

Prefixes a validation with an indexed branch.

Parameters

index: The branch index.
validation: The validation to scope.

Returns

A validation whose diagnostics are prefixed with Index index.

FsFlow.ValidationModule.key

Mon, 01 Jan 0001 00:00:00 +0000

Prefixes a validation with a keyed branch.

Parameters

key: The branch key.
validation: The validation to scope.

Returns

A validation whose diagnostics are prefixed with Key key.

FsFlow.ValidationModule.map

Mon, 01 Jan 0001 00:00:00 +0000

Maps the successful value of a validation.

Parameters

mapper: A function of type 'value -> 'next.
validation: The source Validation.

Returns

A validation with the transformed success value.

FsFlow.ValidationModule.map2

Mon, 01 Jan 0001 00:00:00 +0000

Combines two validations, accumulating errors if both fail.

Remarks

This is the core applicative operation. If both left and right fail, their diagnostics graphs are merged.

Parameters

mapper: A function of type 'left -> 'right -> 'value.
left: The first validation.
right: The second validation.

Returns

A validation with the combined result.

FsFlow.ValidationModule.map3

Mon, 01 Jan 0001 00:00:00 +0000

Combines three validations, accumulating errors when any input fails.

Parameters

mapper: A function of type 'left -> 'middle -> 'right -> 'value.
left: The first validation.
middle: The second validation.
right: The third validation.

Returns

A validation with the combined result.

FsFlow.ValidationModule.mapError

Mon, 01 Jan 0001 00:00:00 +0000

Maps the error type of a validation graph.

Parameters

mapper: A function of type 'error -> 'nextError.
validation: The source Validation.

Returns

A validation with transformed error values.

FsFlow.ValidationModule.merge

Mon, 01 Jan 0001 00:00:00 +0000

Merges two validations into a validation of a tuple.

Parameters

left: The first validation.
right: The second validation.

Returns

A validation containing a tuple of the results.

FsFlow.ValidationModule.name

Mon, 01 Jan 0001 00:00:00 +0000

Prefixes a validation with a named branch.

Parameters

name: The branch name.
validation: The validation to scope.

Returns

A validation whose diagnostics are prefixed with Name name.

FsFlow.ValidationModule.ok

Mon, 01 Jan 0001 00:00:00 +0000

Creates a successful validation result.

Parameters

value: The success value of type 'value.

Returns

A successful Validation.

FsFlow.ValidationModule.orElse

Mon, 01 Jan 0001 00:00:00 +0000

Falls back to another validation when the source validation fails.

Remarks

This is a left-biased choice operator. If the source succeeds, the fallback is not used. If the source fails, the fallback validation is returned as-is.

Parameters

fallback: The validation to use when the source fails.
validation: The source validation.

Returns

The source validation when it succeeds, otherwise the fallback validation.

FsFlow.ValidationModule.orElseWith

Mon, 01 Jan 0001 00:00:00 +0000

Computes a fallback validation from the source diagnostics when validation fails.

Remarks

This is the lazy counterpart to orElse and is useful when the alternate branch depends on the accumulated diagnostics.

Parameters

fallback: A function that turns the diagnostics into an alternate validation.
validation: The source validation.

Returns

The source validation when it succeeds, otherwise the computed fallback validation.

FsFlow.ValidationModule.sequence

Mon, 01 Jan 0001 00:00:00 +0000

Transforms a sequence of validations into a validation of a list.

Parameters

validations: The input sequence.

Returns

A validation containing the list of values.

FsFlow.ValidationModule.succeed

Mon, 01 Jan 0001 00:00:00 +0000

Alias for ok.

Parameters

value: The success value of type 'value.

Returns

A successful Validation.

FsFlow.ValidationModule.toResult

Mon, 01 Jan 0001 00:00:00 +0000

Converts a Validation into a standard Result.

Parameters

validation: The validation to convert.

Returns

A result containing either the success value or the full diagnostics graph.

FsFlow.ValidationModule.traverseIndexed

Mon, 01 Jan 0001 00:00:00 +0000

Maps a sequence into validations while prefixing each item with its index.

Remarks

This is the indexed version of sequence. It is useful for list and array validation because each item can keep its own Index branch without the caller manually wrapping every item.

Parameters

binder: A function of type int -> 'source -> Validation<'value, 'error>.
values: The input sequence.

Returns

A validation containing the list of values or accumulated diagnostics.

FsFlow.Builders.validate

Mon, 01 Jan 0001 00:00:00 +0000

The accumulating validate { } computation expression.

Remarks

Use this builder when you want to collect all validation failures instead of stopping at the first one. Use `and!` when sibling validations should accumulate into the same diagnostics graph. Plain `let!` and `do!` are sequential: if the left side fails, the later step is not evaluated. `Check<'value>` covers both value-preserving checks and gate checks. Use `Check.orError` to attach an application error, and `Guard.Of` / `Guard.MapError` when you want the same error-bound source shape to participate directly in validation. When nested API response fields need to keep their place in the diagnostics graph, use the scoped helpers `validate.key`, `validate.index`, and `validate.name` inside the computation expression. If you already have a `Validation` value, use `Validation.key`, `Validation.index`, or `Validation.name` to prefix it after the fact. It is intended for forms, configuration checks, and other input-heavy boundaries where the user benefits from seeing every problem at once.

Examples

 let validatedUser =
     validate {
         let! name = Check.notBlank input.Name
         let! age = Check.okIf (input.Age > 0) "Age must be positive"
         return { Name = name; Age = age }
     }

let validatedCustomer =
    validate.key "customer" {
        let! name =
            validate.name "Name" {
                return! input.Name |> Check.notBlank |> Check.orError "Name required"
            }

        return name
    }

validate { }

Mon, 01 Jan 0001 00:00:00 +0000

The validate { } builder is used for accumulating sibling failures into a structured diagnostics graph.

Builder

FsFlow.Builders.validate: The accumulating validate { } computation expression.

FsFlow.Validation

Mon, 01 Jan 0001 00:00:00 +0000

An accumulating validation result that keeps the structured diagnostics graph visible.

Remarks

Unlike FSharpResult, this type is designed for applicative composition using and! in the validate { } builder, which merges errors instead of short-circuiting.