42 lines
1 KiB
Text
42 lines
1 KiB
Text
namespace Tutorial
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/- This file contains the code examples that are used in the
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monad control docstring in "How `MonadControl` works" in src/Init/Control/Basic.lean -/
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def σ := Nat
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@[reducible]
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def β := String
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opaque foo : ∀ {α}, IO α → IO α
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opaque bar : StateT σ IO β
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def mapped_foo : StateT σ IO β := do
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let s ← get
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let (b, s') ← liftM <| foo <| StateT.run bar s
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set s'
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return b
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def stM (α : Type) := α × σ
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def restoreM (x : IO (stM α)) : StateT σ IO α := do
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let (a,s) ← liftM x
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set s
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return a
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def mapped_foo' : StateT σ IO β := do
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let s ← get
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let mapInBase := fun z => StateT.run z s
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restoreM <| foo <| mapInBase bar
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def control {α : Type}
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(f : ({β : Type} → StateT σ IO β → IO (stM β)) → IO (stM α))
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: StateT σ IO α := do
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let s ← get
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let mapInBase := fun {β} (z : StateT σ IO β) => StateT.run z s
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let r : IO (stM α) := f mapInBase
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restoreM r
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def mapped_foo'' : StateT σ IO β :=
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control (fun mapInBase => foo (mapInBase bar))
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end Tutorial
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