Haskell as a JavaScript MVC framework

Github link is broken .org instead of .com https://github.com/tonyday567/mvc-todo

That is something I was worried about, because afaik, ghcjs is still fairly experimental. But ability to use ghc's magic to produce javascript sounds aluring :-)

I think, that if you could integrate source-map capabilities (haven't tried http://hackage.haskell.org/package/sourcemap yet) it might make the debug process more bearable.

But if you would be looking for haskell-like-language with more comprehensible to-javascript output, http://www.purescript.org/ pleasantly suprised me (even though I had time to barely get past the hello world :-)

And the actual Action sumtype is here:

https://github.com/tonyday567/mvc-todo/blob/cb4bbb613aa31ba6...

I'm a big fan of static typing, including sum types. But can someone explain to me what's so great here?

The highlight of the article is having a unique Action sum type instead of a myriad of separate functions. But the action still has to be processed by a myriad of separate equations (is that the correct Haskell term? Not familiar with the language):

    apply ClearCompleted tds = over todosItems (Map.filter (\x -> view itemStatus x /= Completed)) tds
    apply (DeleteItem x) tds = over todosItems (Map.delete x) tds
    apply (EditItem x) tds = set todosEditing (Just x) tds
    ...

"Only one of the 68 frameworks defined an Action" is probably because it's simpler to directly call the right function, rather than over-engineering things with a short-lived intermediary representation.

If actions need to "be serialized, recorded for later analytics, and generated automatically" then it makes much more sense. But this is a TODO sample app. YAGNI.

And if we really need it, it's not like JS cannot do it:

    function apply(action, todos) {
        switch (action.type) {
            case 'ClearCompleted':
                return todos.filter(todo => !todo.completed);
            case 'DeleteItem':
                return todos.filter(todo => todo !== action.todo);
            ...
        }
    }

The above has probably been done a billion times in one form or another. Of course it's not safe from typos in the case strings or missing cases, but that's a broader issue with JS in general, not specifically related to sum types.

I'm not trying to shoot down Haskell here, I really wish someone will point to something I'm missing and make it click. But right now it just looks like over-engineering that JS could do but chooses not to.

(Regarding footnote #4: Swift also has sum types and is fairly popular.)

Yikes, 1,670KB for generated javascript alone, that's kind of a deal breaker.

GHCJS has a ways to go methinks. Js_of_ocaml and Scala.js are far better suited for production use today as the type safety "tax" is much smaller (i.e. binary is at most 1/4 the size for equivalent functionality).

EDIT:

didn't realize you cannot yet call into Haskell from GHCJS, and even Haskell to GHCJS requires going through FFI[1]

Meh, might as well use Fay or Haste if that's the caste.

[1] http://stackoverflow.com/questions/29967135/how-to-call-hask...