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Update state.md #2248

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Jun 11, 2018
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Update state.md #2248

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85a920a
Update state.md
rsekulski May 6, 2018
967c869
Added code which presents type safety of IndexedStateT
rsekulski May 31, 2018
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12 changes: 10 additions & 2 deletions docs/src/main/tut/datatypes/state.md
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Original file line number Diff line number Diff line change
Expand Up @@ -282,8 +282,8 @@ So, let's model our typed door:
import cats.Eval
import cats.data.IndexedStateT

def open: IndexedStateT[Eval, Open.type, Closed.type, Unit] = IndexedStateT.set(Closed)
def close: IndexedStateT[Eval, Closed.type, Open.type, Unit] = IndexedStateT.set(Open)
def open: IndexedStateT[Eval, Closed.type, Open.type, Unit] = IndexedStateT.set(Open)
def close: IndexedStateT[Eval, Open.type, Closed.type, Unit] = IndexedStateT.set(Closed)
```

We can now reject, at compile time, sequences of `open` and `close` that are invalid:
Expand All @@ -305,3 +305,11 @@ val valid = for {
```

Note that the inferred type of `valid` correctly models that this computation can be executed only with an initial `Closed` state.

```tut:book:fail
valid.run(Open)
```

```tut:book
valid.run(Closed)
```