Created
June 19, 2016 08:11
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Generate Trees in Elm
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| import Html exposing (Html, text, div, button) | |
| import Html.App exposing (beginnerProgram) | |
| import Html.Events exposing (onClick) | |
| import Random exposing (Generator, Seed, step, initialSeed, andThen, map, map2, int) | |
| main = | |
| beginnerProgram { | |
| model = init 0 | |
| , view = view | |
| , update = update | |
| } | |
| type Tree = | |
| Leaf Int | |
| | Node Tree Tree | |
| tree : Generator Tree | |
| tree = | |
| let | |
| createNode left right = | |
| Node left right | |
| selectTreeGenerator : Int -> Generator Tree | |
| selectTreeGenerator n = | |
| case n of | |
| 0 -> map2 createNode tree tree | |
| _ -> map (\n -> Leaf n) (int 0 10) | |
| in | |
| (int 0 2) `andThen` selectTreeGenerator | |
| type alias Model = { tree : Tree, seed : Seed } | |
| init : Int -> Model | |
| init n = | |
| let | |
| seed = initialSeed n | |
| (t, seed') = step tree seed | |
| in | |
| { tree = t, seed = seed' } | |
| type Message = | |
| DoNothing | |
| | GenerateTree | |
| update : Message -> Model -> Model | |
| update message model = | |
| case message of | |
| DoNothing -> model | |
| GenerateTree -> | |
| let | |
| (t, seed') = step tree model.seed | |
| in | |
| { model | tree = t, seed = seed' } | |
| view : Model -> Html Message | |
| view model = | |
| div [] [ | |
| button [onClick GenerateTree ] [ text "go" ] | |
| , text (toString model.tree) | |
| ] |
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