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simple type-level state machine in elm. invalid tra
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| module Machine exposing (..) | |
| type DoorState = Opened | Closed | |
| type ClosedDoor = ClosedDoor DoorState | |
| type OpenedDoor = OpenedDoor DoorState | |
| closed : ClosedDoor | |
| closed = ClosedDoor Closed | |
| opened : OpenedDoor | |
| opened = OpenedDoor Opened | |
| close : OpenedDoor -> ClosedDoor | |
| close opened_door = closed | |
| open : ClosedDoor -> OpenedDoor | |
| open closed_door = opened | |
| sequence : ClosedDoor -> ClosedDoor | |
| sequence = open >> close >> open >> close | |
| test : ClosedDoor | |
| test = sequence closed | |
| -- bad = closed |> close |
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