dispatch method in view for parent child composition - f#

I am trying to understand the way fable is supposed to work with parent child composition. Things are quite easy when it comes to update method, init, and the definition of commands. But the view method and its dispatch method are tricky to find out
In my code, the child is:
module DeploymentView
type DeploymentTypeView =
| DeployContainerView
type Model = {
CurrentView : DeploymentTypeView option
}
type Msg =
| ShowDeployContainer
let init () : Model =
let initialModel = {
CurrentView = None
}
initialModel
let update (msg : Msg) (currentModel : Model) : Model * Cmd<Msg> =
match msg with
| ShowDeployContainer ->
let nextModel = {
currentModel with CurrentView = Some DeployContainerView
}
nextModel, Cmd.none
| _ -> currentModel, Cmd.none
let view (model : Model) (dispatch : Msg -> unit) =
[
Content.content [ Content.Modifiers [ Modifier.TextAlignment (Screen.All, TextAlignment.Left) ] ]
[
Heading.h3 [] [ str ("Deployments: ") ]
]
Columns.columns []
[
Column.column [] [ button "deploy container" (fun _ -> dispatch ShowDeployContainer) ]
]
]
And following this documentation about parent child processing I have define a parent like this one:
module Client
type PortalView =
| DeploymentView of DeploymentView.Model
| ProductAdministrationView
type Model = {
CurrentPortal : PortalView option
}
// The Msg type defines what events/actions can occur while the application is running
// the state of the application changes *only* in reaction to these events
type Msg =
| ShowDeployment
| ShowAdministration
| DeployContainerView of DeploymentView.Msg
// defines the initial state and initial command (= side-effect) of the application
let init () : Model * Cmd<Msg> =
let initialModel = {
CurrentPortal = None
}
initialModel, Cmd.none
let update (msg : Msg) (currentModel : Model) : Model * Cmd<Msg> =
match msg with
| ShowDeployment ->
let nextModel = {
currentModel with CurrentPortal = Some <| DeploymentView(DeploymentView.init())
}
nextModel, Cmd.none
| ShowAdministration ->
let nextModel = {
currentModel with CurrentPortal = Some ProductAdministrationView
}
nextModel, Cmd.none
| DeployContainerView msg' ->
let res, cmd =
match currentModel.CurrentPortal with
| Some(DeploymentView(m)) -> DeploymentView.update msg' m
| _ -> DeploymentView.init(), Cmd.none
{ currentModel with CurrentPortal = Some(DeploymentView(res)) }, Cmd.map DeployContainerView cmd
So far so good, my issue comes when it goes to the rendering of the view itself.
The client view uses a function as follows:
let view (model : Model) (dispatch : Msg -> unit)
where Msg is of type DeploymentView.Msg whereas in the parent view I have access to a dispatch of type Client.Msg -> unit. how can I decompose the parent dispatch to map it to the child dispatch signature?

You can very easily create a dispatch function that conforms to what the child expects by using the >> operator:
DeploymentView.view deploymentViewModel (DeployContainerView >> dispatch)
which is equivalent to doing:
DeploymentView.view deploymentViewModel (fun msg -> msg |> DeployContainerView |> dispatch)
That is, it wraps the child's message in DeployContainerView, then passes that to dispatch.
On another note, it is a common and good convention to use a Msg suffix on constructors used to wrap child msg types. You may want to consider renaming DeployContainerView to DeploymentContainerMsg.

Related

FsCheck lazy generators

I have issues with generation of data within my tests.
testProperty "calculate Operation against different operations should increase major" <| fun operationIdApi operationIdClient summaryApi summaryClient descriptionApi descriptionClient ->
( notAllEqual [
fun () -> assessEquality <| StringEquals(operationIdApi, operationIdClient)
fun () -> assessEquality <| StringEquals(summaryApi , summaryClient)
fun () -> assessEquality <| StringEquals(descriptionApi, descriptionClient)
]) ==> lazy (
let operationClient = createOpenApiOperation operationIdClient summaryClient descriptionClient
let operationAPI = createOpenApiOperation operationIdApi summaryApi descriptionApi
let actual = calculate operationAPI operationClient
Expect.equal actual (Fact.Semver.IncreaseMajor) "return IncreaseMajor"
)
The code that is actually tested is :
semver {
if operationAPI.OperationId<> operationClient.OperationId then yield! IncreaseMajor
if operationAPI.Summary <> operationClient.Summary then yield! IncreaseMajor
}
The test should fail when the data produced is same OperationId, same summary and different description.
But it does not and it led me to create my own generator or at least try to do so:
I wanted my test to be written like this :
testProperty "calculate Operation against different operations should increase major" <| fun (operationId:ElementSet<string>) (summary:ElementSet<string>) ->
Therefore I create a type accordingly:
type ElementSet<'a> =
| Same of 'a
| Different
and a generator for this type :
let setGen<'a> =
Gen.oneof [
gen {
let! v = Arb.generate<'a>
return Same(v)
}
gen { return Different}
]
type ElementSetGenerator =
static member ElementSet() =
Arb.fromGen setGen<'a>
do Arb.register<ElementSetGenerator>() |> ignore
I was then trying to extract the data to construct my object :
let createOpenApiOperation operationId summary=
let pi = OpenApiOperation(OperationId=operationId.Get, Summary=summary.Get)
pi
The Get method did not exist yet so I was about to implement it by adding a member to my ElementSet<'a>:
type ElementSet<'a> =
| Same of 'a
| Different
with member this.Get =
match this with
| Same s -> s
| Different -> Arb.generate<'a>// some random generation here
And this is where I am stuck. I would love to get some randomness here when I extract data. I wonder if this is the correct way to do so, or if I should have answered the problem earlier?
Thanks for your inputs.
I think I found it, the answer was to handle it at the beginning :
let setGen<'a when 'a:equality> =
Gen.oneof [
gen {
let! v = Arb.generate<'a>
return Same(v)
}
gen {
let! x,y =
Arb.generate<'a>
|> Gen.two
|> Gen.filter (fun (a,b)-> a <> b)
return Different(x,y)
}
]
and then to use two getter to access the values :
type ElementSet<'a> when 'a:equality=
| Same of 'a
| Different of 'a*'a
with member this.Fst = match this with | Same s -> s | Different (a, b)-> a
member this.Snd = match this with | Same s -> s | Different (a, b)-> b
this way I can access values within my test:
testProperty "calculate Operation against different operations should increase major" <| fun (operationId:ElementSet<NonWhiteSpaceString>) (summary:ElementSet<NonWhiteSpaceString>) (description:ElementSet<NonWhiteSpaceString>) ->
let operationClient = createOpenApiOperation operationId.Fst summary.Fst description.Fst
let operationAPI = createOpenApiOperation operationId.Snd summary.Snd description.Snd
let actual = calculate operationAPI operationClient
Expect.equal actual (Fact.Semver.IncreaseMajor) "return IncreaseMajor"
for the record I then have the creation of my stub as follows :
let createOpenApiOperation (operationId:NonWhiteSpaceString) (summary:NonWhiteSpaceString) (description:NonWhiteSpaceString)=
let pi = OpenApiOperation(OperationId=operationId.Get, Summary=summary.Get, Description=description.Get)
pi

How to implement Task.Map

Have I correctly implemented map for Task?
let map continuation (t: Task<'A>) =
t.ContinueWith(fun (antecedent: Task<'A>) ->
if antecedent.Status <> TaskStatus.Canceled &&
antecedent.Status <> TaskStatus.Faulted then
continuation antecedent.Result
else
raise antecedent.Exception // must I?
)
I got the TaskStatus checks from the docs. I feel most uncertain about raise antecedent.Exception, but I can't think of another way to handle it.
As background, yes I'm aware of Async, but my current stack uses Entity Framework and Blazor, so I have a backend that uses things like .ToListAsync() and a front end in C#, so I'd rather just not deal with converting from Task to Async then back again.
I would suggest implementing your solution in terms of the interfaces behind the concept of awaitable in the TPL, namely INotifyCompletion and ICriticalNotifyCompletion. Also, to implement map correctly, you should really do it in terms of bind. This is something that there are already some existing solutions for in F#, such as the TaskBuilder library. Personally, I have been using the following in a library for years without any issues:
open System.Runtime.CompilerServices
open System.Threading.Tasks
type TaskStep<'result> =
| Value of 'result
| AsyncValue of 'result Task
| Continuation of ICriticalNotifyCompletion * (unit -> 'result TaskStep)
and StateMachine<'a>(firstStep) as this =
let methodBuilder = AsyncTaskMethodBuilder<'a Task>()
let mutable continuation = fun () -> firstStep
let nextAwaitable() =
try
match continuation() with
| Value r ->
methodBuilder.SetResult(Task.FromResult(r))
null
| AsyncValue t ->
methodBuilder.SetResult(t)
null
| Continuation (await, next) ->
continuation <- next
await
with
| exn ->
methodBuilder.SetException(exn)
null
let mutable self = this
member __.Run() =
methodBuilder.Start(&self)
methodBuilder.Task
interface IAsyncStateMachine with
member __.MoveNext() =
let mutable await = nextAwaitable()
if not (isNull await) then
methodBuilder.AwaitUnsafeOnCompleted(&await, &self)
member __.SetStateMachine(_) =
()
type Binder<'out> =
static member inline GenericAwait< ^abl, ^awt, ^inp
when ^abl : (member GetAwaiter : unit -> ^awt)
and ^awt :> ICriticalNotifyCompletion
and ^awt : (member get_IsCompleted : unit -> bool)
and ^awt : (member GetResult : unit -> ^inp) >
(abl : ^abl, continuation : ^inp -> 'out TaskStep) : 'out TaskStep =
let awt = (^abl : (member GetAwaiter : unit -> ^awt)(abl))
if (^awt : (member get_IsCompleted : unit -> bool)(awt))
then continuation (^awt : (member GetResult : unit -> ^inp)(awt))
else Continuation (awt, fun () -> continuation (^awt : (member GetResult : unit -> ^inp)(awt)))
module TaskStep =
let inline bind f step : TaskStep<'a> =
Binder<'a>.GenericAwait(step, f)
let inline toTask (step: TaskStep<'a>) =
try
match step with
| Value x -> Task.FromResult(x)
| AsyncValue t -> t
| Continuation _ as step -> StateMachine<'a>(step).Run().Unwrap()
with
| exn ->
let src = new TaskCompletionSource<_>()
src.SetException(exn)
src.Task
module Task =
let inline bind f task : Task<'a> =
TaskStep.bind f task |> TaskStep.toTask
let inline map f task : Task<'b> =
bind (f >> Value) task
FsToolkit.ErrorHandling implements it here. I'll paste the current version below as it's quite short. It uses the TaskBuilder library Aaron mentioned.
module Task =
let singleton value = value |> Task.FromResult
let bind (f : 'a -> Task<'b>) (x : Task<'a>) = task {
let! x = x
return! f x
}
let map f x = x |> bind (f >> singleton)
Additionally, FSharpPlus has an independent implementation of Task.map here.
Throwing the exception again in the continuation would make for an incorrect stack trace.
It's a mapping from 'A -> 'B, so it's probably best to lay it out explicitly.
let rec map (continuation: 'A -> 'B) (t: Task<'A>) =
let rec map_resolved (task: Task<'A>) =
match task.Status with
| TaskStatus.RanToCompletion -> Task.FromResult(continuation task.Result)
| TaskStatus.Faulted -> Task.FromException<'B>(task.Exception)
| TaskStatus.Canceled -> Task.FromCanceled<'B>(CancellationToken.None)
| _ -> task.ContinueWith(map_resolved).Unwrap()
map_resolved t

How to encapsulate logic within children like component frameworks?

I'm trying to understand how to create reusable components using the Elmish architecture within F# Bolero by WebSharper (e.g. a reusable validated form input). From all of the examples I've seen, the top level Parent must handle all messages/updates and logic, while children are simply for views. I'm wondering if there's a way around this, whether by having a child handle its own state + messages, and propagating certain messages to the parent (which I've attempted in code below), or if there's another design to handle this.
In my specific case, I'm trying to create a form input component for a users name that validates neither field is empty. I don't like the idea of having a parent handle updating the individual fields FirstName and LastName, it should only care about picking up the Submit message. Handling every message a child produces would results in a ton of boilerplate if you use the child more than once
Note: The code I've provided does not compile as I'm struggling to understand how to implement my intended design
open Elmish
open Bolero
open Bolero.Html
module NameInput =
type Model = { FirstName : string; LastName : string }
type Message =
| ChangeFirstName of string
| ChangeLastName of string
| Submit of Model
let update model msg =
match msg with
| ChangeFirstName s ->
{ model with FirstName = s}, Cmd.none
| ChangeLastName s ->
{ model with LastName = s}, Cmd.none
| Submit m ->
m, Cmd.ofMsg (Submit m)
type Component() =
inherit ElmishComponent<Message, Model>()
let invalidField s = s <> ""
override this.View model dispatch =
let fnClass = if (invalidField model.FirstName) then "invalid" else "valid"
let lnClass = if (invalidField model.LastName) then "invalid" else "valid"
div [] [
label [] [ text "First Name: " ]
input [
attr.``class`` fnClass
on.change (fun e -> update model (ChangeFirstName (unbox e.Value)))
]
label [] [ text "Last Name: " ]
input [
attr.``class`` lnClass
on.change (fun e -> update model (ChangeLastName (unbox e.Value)))
]
button [ on.click (fun _ -> update model (Submit model)) ] [ text "Submit" ]
]
type Message =
| NameSubmitted of NameInput.Message.Submit
type Model = { UserName : NameInput.Model }
let initModel = { UserName = { FirstName = ""; LastName = "" } }
let update msg model =
match msg with
| NameSubmitted name ->
// Greet the user
{ model with UserName = name }, Cmd.none
let view model dispatch =
concat [
ecomp<NameInput.Component,_,_>
model.Username dispatch
]
type MyApp() =
inherit ProgramComponent<Model, Message>()
override this.Program =
Program.mkProgram (fun _ -> initModel, Cmd.none) update view
Thank you #rmunn and #hvester for the references, it helped me get a better understanding of Elmish and was able to come up with a solution. As a reference for anyone else who may stumble across this, here is the solution. InternalMessage does not need to private, it just hides those cases from the main program's update function so one can easily see which messages they need to handle. If it is public though, compiler will give an error if you try to match on an InternalMessage case without first unwrapping the Message into an InternalMessage (so the programmer still easily knows which messages are internal)
module NameInput =
type Model = { FirstName : string; LastName : string }
type private InternalMessage =
| ChangeFirstName of string
| ChangeLastName of string
type Message =
| Internal of InternalMessage
| Submit of Model
let update msg model =
match msg with
| ChangeFirstName s ->
{ model with FirstName = s }
| ChangeLastName s ->
{ model with LastName = s }
type Component() =
inherit ElmishComponent<Model, Message>()
let invalidField s = s <> ""
override this.View model dispatch =
let fnClass = if (invalidField model.FirstName) then "invalid" else "valid"
let lnClass = if (invalidField model.LastName) then "invalid" else "valid"
div [] [
label [] [ text "First Name: " ]
input [
attr.``class`` fnClass
on.change (fun e -> dispatch << Internal << ChangeFirstName <| unbox e.Value)
]
label [] [ text "Last Name: " ]
input [
attr.``class`` lnClass
on.change (fun e -> dispatch << Internal << ChangeLastName <| unbox e.Value)
]
button [ on.click (fun _ -> dispatch <| Submit model) ] [ text "Submit" ]
]
type Model = { Name : NameInput.Model }
let initModel = { Name = { FirstName = ""; LastName = "" } }
type Message =
| NameInput of NameInput.Message
let update message model =
match message with
| NameInput ni ->
match ni with
| NameInput.Internal i ->
{ model with Name = model.Name |> NameInput.update i}
| NameInput.Submit n ->
{ model with Name = n }

Elmish dispatch on Fable React stateful component

I need to use Fable-React stateful component with elmish dispatch. I can not figure out how to create it.
I am using this project template: https://github.com/fable-elmish/templates
here is model:
module Home.Types
[<Pojo>]
type Model = {
isLoading: bool
}
here is the component:
type Documentation(props) as this =
inherit Component<Documentation.Types.Model,obj>(props)
do
()
override this.componentWillMount () =
printfn "componentWillMount"
**RequestProcessDocumentation |> dispatch <-- this is what I need**
override this.render() =
printfn "render"
let (?) = Fable.Core.JsInterop.(?)
div []
[
p [] [str(this.props.isLoading.ToString())]
button [ OnClick (fun _ -> RequestProcessDocumentation |> dispatch ) ] [str("Click me")]
]
how can I create it using ofType function, so then I can use it like this:
let pageHtml =
function
| Home -> Home.View.root model.home (HomeMsg >> dispatch)
| Documentation -> documentation (DocumentationMsg >>
I added the dispatch function to props:
[<Pojo>]
type Model = {
isLoading: bool
processDocumentation: ProcessDocumentationDto
valuesForFilterDropdown: DropdownFilterValues
scopeOfFilter: ScopeOfFilter
expandedMenuItemsIds: string list
}
[<Pojo>]
type DocumentationProps = {
model: Model
dispatch: Msg -> unit
}
create the view:
let root model dispatch =
let inline documentation props = ofType<Documentation,_,_> props []
let pageHtml =
function
| Home -> Home.View.root model.home (HomeMsg >> dispatch)
| Documentation -> documentation { model.documentation with dispatch = (DocumentationMsg >> dispatch)}
and then I call it this way:
RequestProcessDocumentation |> this.props.dispatch

Avoiding nested pattern matching (possibly with maybe monad)

How could nested pattern matching, such as the following example, be re-written so that None is specified only once? I think the Maybe monad solves this problem. Is there something similar in the F# core library? Or, is there an alternative approach?
match a with
| Some b ->
let c = b.SomeProperty
match c with
| Some d ->
let e = d.SomeProperty
//and so on...
| None -> ()
| None -> ()
you can solve this using built-in capabilities: Option.bind
type A =
member this.X : B option = Unchecked.defaultof<_>
and B =
member this.Y : С option = Unchecked.defaultof<_>
and С =
member this.Z : string option = Unchecked.defaultof<_>
let a : A = Unchecked.defaultof<_>
let v =
match
a.X
|> Option.bind (fun v -> v.Y)
|> Option.bind (fun v -> v.Z) with
| Some s -> s
| None -> "<none>"
Frankly, I doubt that introducing full-fledged 'maybe' implementation (via computation expressions) here can shorten the code.
EDIT: Dream mode - on
I think that version with Option.bind can be made smaller if F# has more lightweight syntax for the special case: lambda that refer to some member of its argument:
"123" |> fun s -> s.Length // current version
"123" |> #.Length // hypothetical syntax
This is how the sample can be rewritten in Nemerle that already has such capabilities:
using System;
using Nemerle.Utility; // for Accessor macro : generates property for given field
variant Option[T]
{
| Some {value : T}
| None
}
module OptionExtensions
{
public Bind[T, U](this o : Option[T], f : T -> Option[U]) : Option[U]
{
match(o)
{
| Option.Some(value) => f(value)
| Option.None => Option.None()
}
}
}
[Record] // Record macro: checks existing fields and creates constructor for its initialization
class A
{
[Accessor]
value : Option[A];
}
def print(_)
{
// shortened syntax for functions with body -> match over arguments
| Option.Some(_) => Console.WriteLine("value");
| Option.None => Console.WriteLine("none");
}
def x = A(Option.Some(A(Option.Some(A(Option.None())))));
print(x.Value.Bind(_.Value)); // "value"
print(x.Value.Bind(_.Value).Bind(_.Value)); // "none"
I like desco's answer; one should always favor built-in constructs. But FWIW, here's what a workflow version might look like (if I understand the problem correctly):
type CE () =
member this.Bind (v,f) =
match v with
| Some(x) -> f x
| None -> None
member this.Return v = v
type A (p:A option) =
member this.P
with get() = p
let f (aIn:A option) = CE () {
let! a = aIn
let! b = a.P
let! c = b.P
return c.P }
let x = f (Some(A(None)))
let y = f (Some(A(Some(A(Some(A(Some(A(None)))))))))
printfn "Your breakpoint here."
I don't suggest this, but you can also solve it with exception handling:
try
<code that just keeps dotting into option.Value with impunity>
with
| :? System.NullReferenceException -> "None"
I just wanted to point out the rough equivalence of exception-handling to the Maybe/Either monads or Option.bind. Typically prefer one of them to throwing and catching exceptions.
Using Option.maybe from FSharpx:
open FSharpx
type Pet = { Name: string; PreviousOwner: option<string> }
type Person = { Name: string; Pet: option<Pet> }
let pers = { Name = "Bob"; Pet = Some {Name = "Mr Burns"; PreviousOwner = Some "Susan"} }
Option.maybe {
let! pet = pers.Pet
let! prevOwner = pet.PreviousOwner
do printfn "%s was the previous owner of %s." prevOwner pet.Name
}
Output:
Susan was the previous owner of Mr Burns.
But, e.g. with this person instead there is just no output:
let pers = { Name = "Bob"; Pet = None }

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