Validating Signals

Signals in Gjallarhorn also provide a mechanism to filter based on validation rules. A review of the basics of validation in Gjallarhorn prior to reading this section will be beneficial.

Signal.validate allows you to filter a Signal into an IValidatedSignal<'a,'b>, which provides the following new properties:

ValidationResult: a ISignal<ValidationResult> with details of the validation of the current value of the view
IsValid: a boolean of whether the current view's value is valid
RawInput: a ISignal<'a> with the raw, unvalidated input

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#r "Gjallarhorn.dll"

open Gjallarhorn

open Gjallarhorn.Validation
open Gjallarhorn.Validation.Validators

let source = Mutable.create 0

// Create a Signal on the mutable, validating it with 3 rules on the fly:
let test = Signal.validate (notEqual 3 >> greaterThan 1 >> lessThan 5) source

// Prints: Valid?: false
printfn "Valid?: %b" test.IsValid

source.Value <- 2
// Prints: Valid?: true
printfn "Valid?: %b" test.IsValid

source.Value <- 3
// Prints: Validation: Invalid ["Value cannot equal 3"]
printfn "Validation: %A" test.ValidationResult.Value
// Prints: Raw (unvalidated) input: 3
printfn "Raw (unvalidated) input: %A" test.RawInput.Value

val source : obj

Full name: Validate_types.source

val test : obj

Full name: Validate_types.test

val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn