gistfile1.txt

module Marick where

maybe : b -> (a -> b) -> Maybe a -> b
maybe x f m =
    case m of
        Nothing -> x
        Just y -> f y


type Model = Model
type Form = Form
type Animal = Animal

type Op = CancelEdits
        | StartSavingEdits

upsertAnimal : Animal -> Model -> Model
upsertAnimal _ m = m

originalAnimal : Form -> Maybe Animal
originalAnimal Form = Just Animal

noCmd : Model -> Model
noCmd m = m

id : a -> a
id x = x

runOp : Model -> Form -> Op -> Model
runOp model form op =
    let original = originalAnimal form in
    case op of
        CancelEdits -> model |>  maybe id upsertAnimal original |> noCmd