Samuel Laurén Soft
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| -- in reply to http://www.reddit.com/r/haskell/comments/21mja6/make_lllegal_state_transitions_unrepresentable/ | |
| -- | |
| -- We implement a tiny language with three commands: Open, Close, and Get. | |
| -- The first Get after an Open returns 1, the second Get returns 2, and so on. | |
| -- | |
| -- Get is only valid while the state is open, and | |
| -- Open must always be matched by a Close. | |
| -- We enforce both restrictions via the type system. | |
| -- | |
| -- There are two valid states: Opened and Closed. |