This is an example of coding a state machine in Elm.
For a better example, see this one: [ https://gist.github.com/rupertlssmith/88946c8d207d7ad64daf4360fef1ac42 ]
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January 11, 2018 16:19
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Experimenting with state machines in Elm
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| type alias WithContent = | |
| { contentItem : Content } | |
| type alias WithSelectedModel = | |
| { contentModel : ContentModel | |
| , overlay : Overlay.Model | |
| } | |
| type alias WithInlineEditor = | |
| { inlineEditorStyle : Animation.State | |
| } | |
| type Mode | |
| = Loading | |
| | Explore WithContent | |
| | Markdown WithContent WithSelectedModel | |
| | Preview WithContent WithSelectedModel | |
| | Wysiwyg WithContent WithSelectedModel WithInlineEditor | |
| type alias Model = | |
| { mode : Mode | |
| , menu : Menu | |
| } | |
| maybeLoading : Mode -> Maybe Mode | |
| maybeLoading state = | |
| case state of | |
| Loading -> | |
| Just state | |
| _ -> | |
| Nothing | |
| -- ... more maybeState functions | |
| mapWhenWithContent : (WithContent -> a) -> Mode -> Maybe a | |
| mapWhenWithContent func state = | |
| case state of | |
| Explore content -> | |
| Just <| func content | |
| Markdown content _ -> | |
| Just <| func content | |
| Preview content _ -> | |
| Just <| func content | |
| Wysiwyg content _ _ -> | |
| Just <| func content | |
| _ -> | |
| Nothing | |
| -- ... More mapWhen functions | |
| updateWhenWithContent : (WithContent -> WithContent) -> Mode -> Maybe Mode | |
| updateWhenWithContent func state = | |
| case state of | |
| Explore content -> | |
| func content |> Explore |> Just | |
| Markdown content selected -> | |
| func content |> (flip Markdown) selected |> Just | |
| Preview content selected -> | |
| func content |> (flip Preview) selected |> Just | |
| Wysiwyg content selected inline -> | |
| func content |> (swirll Wysiwyg) selected inline |> Just | |
| _ -> | |
| Nothing | |
| -- ... More updateWhen functions | |
| -- State transition functions - these may contain custom logic, unlike the above which area really just boilerplate. | |
| toLoading : Mode -> Mode | |
| toLoading _ = | |
| Loading | |
| toExplore : WithContent -> Mode -> Maybe Mode | |
| toExplore content state = | |
| case state of | |
| Loading -> | |
| Nothing | |
| _ -> | |
| Explore content |> Just | |
| toMarkdown : WithSelectedModel -> Mode -> Maybe Mode | |
| toMarkdown selected state = | |
| case state of | |
| Loading -> | |
| Nothing | |
| _ -> | |
| mapWhenWithContent | |
| (\content -> | |
| Markdown content selected | |
| ) | |
| state | |
| toPreview : WithSelectedModel -> Mode -> Maybe Mode | |
| toPreview selected state = | |
| case state of | |
| Loading -> | |
| Nothing | |
| _ -> | |
| mapWhenWithContent | |
| (\content -> | |
| Preview content selected | |
| ) | |
| state | |
| toWysiwyg : WithSelectedModel -> WithInlineEditor -> Mode -> Maybe Mode | |
| toWysiwyg selected inline state = | |
| case state of | |
| Loading -> | |
| Nothing | |
| _ -> | |
| mapWhenWithContent | |
| (\content -> | |
| Wysiwyg content selected inline | |
| ) | |
| state | |
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| module StateModel | |
| exposing | |
| ( boolToMaybe | |
| , (>&&>) | |
| , (>||>) | |
| , defaultTransition | |
| , mapWhenCompose | |
| ) | |
| import Maybe exposing (andThen) | |
| import Maybe.Extra exposing (orElse) | |
| boolToMaybe : (a -> Bool) -> a -> Maybe a | |
| boolToMaybe filter val = | |
| if filter val then | |
| Just val | |
| else | |
| Nothing | |
| (>&&>) : (a -> Maybe b) -> (b -> Maybe c) -> a -> Maybe c | |
| (>&&>) fst snd val = | |
| fst val |> andThen snd | |
| (>||>) : (a -> Maybe b) -> (a -> Maybe b) -> a -> Maybe b | |
| (>||>) fst snd val = | |
| fst val |> orElse (snd val) | |
| defaultTransition state trans = | |
| trans state |> Maybe.withDefault state | |
| mapWhenCompose : (c -> d -> Maybe a) -> (a -> d -> Maybe b) -> c -> d -> Maybe b | |
| mapWhenCompose mapWhen1 mapWhen2 func state = | |
| mapWhen1 func state | |
| |> andThen ((flip mapWhen2) state) |
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StateModel.elm contains some helper functions.