162 lines
6 KiB
Text
162 lines
6 KiB
Text
/-
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Copyright (c) 2017 Microsoft Corporation. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Authors: Jared Roesch, Sebastian Ullrich
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The Except monad transformer.
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-/
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prelude
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import Init.Control.Basic
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import Init.Control.Id
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import Init.Coe
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namespace Except
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variable {ε : Type u}
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@[inline] protected def pure (a : α) : Except ε α :=
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Except.ok a
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@[inline] protected def map (f : α → β) : Except ε α → Except ε β
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| Except.error err => Except.error err
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| Except.ok v => Except.ok <| f v
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@[simp] theorem map_id : Except.map (ε := ε) (α := α) (β := α) id = id := by
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apply funext
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intro e
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simp [Except.map]; cases e <;> rfl
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@[inline] protected def mapError (f : ε → ε') : Except ε α → Except ε' α
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| Except.error err => Except.error <| f err
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| Except.ok v => Except.ok v
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@[inline] protected def bind (ma : Except ε α) (f : α → Except ε β) : Except ε β :=
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match ma with
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| Except.error err => Except.error err
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| Except.ok v => f v
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@[inline] protected def toBool : Except ε α → Bool
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| Except.ok _ => true
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| Except.error _ => false
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@[inline] protected def toOption : Except ε α → Option α
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| Except.ok a => some a
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| Except.error _ => none
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@[inline] protected def tryCatch (ma : Except ε α) (handle : ε → Except ε α) : Except ε α :=
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match ma with
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| Except.ok a => Except.ok a
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| Except.error e => handle e
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instance : Monad (Except ε) where
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pure := Except.pure
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bind := Except.bind
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map := Except.map
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end Except
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def ExceptT (ε : Type u) (m : Type u → Type v) (α : Type u) : Type v :=
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m (Except ε α)
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@[inline] def ExceptT.mk {ε : Type u} {m : Type u → Type v} {α : Type u} (x : m (Except ε α)) : ExceptT ε m α := x
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@[inline] def ExceptT.run {ε : Type u} {m : Type u → Type v} {α : Type u} (x : ExceptT ε m α) : m (Except ε α) := x
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namespace ExceptT
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variable {ε : Type u} {m : Type u → Type v} [Monad m]
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@[inline] protected def pure {α : Type u} (a : α) : ExceptT ε m α :=
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ExceptT.mk <| pure (Except.ok a)
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@[inline] protected def bindCont {α β : Type u} (f : α → ExceptT ε m β) : Except ε α → m (Except ε β)
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| Except.ok a => f a
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| Except.error e => pure (Except.error e)
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@[inline] protected def bind {α β : Type u} (ma : ExceptT ε m α) (f : α → ExceptT ε m β) : ExceptT ε m β :=
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ExceptT.mk <| ma >>= ExceptT.bindCont f
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@[inline] protected def map {α β : Type u} (f : α → β) (x : ExceptT ε m α) : ExceptT ε m β :=
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ExceptT.mk <| x >>= fun a => match a with
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| (Except.ok a) => pure <| Except.ok (f a)
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| (Except.error e) => pure <| Except.error e
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@[inline] protected def lift {α : Type u} (t : m α) : ExceptT ε m α :=
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ExceptT.mk <| Except.ok <$> t
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instance : MonadLift (Except ε) (ExceptT ε m) := ⟨fun e => ExceptT.mk <| pure e⟩
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instance : MonadLift m (ExceptT ε m) := ⟨ExceptT.lift⟩
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@[inline] protected def tryCatch {α : Type u} (ma : ExceptT ε m α) (handle : ε → ExceptT ε m α) : ExceptT ε m α :=
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ExceptT.mk <| ma >>= fun res => match res with
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| Except.ok a => pure (Except.ok a)
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| Except.error e => (handle e)
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instance : MonadFunctor m (ExceptT ε m) := ⟨fun f x => f x⟩
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instance : Monad (ExceptT ε m) where
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pure := ExceptT.pure
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bind := ExceptT.bind
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map := ExceptT.map
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@[inline] protected def adapt {ε' α : Type u} (f : ε → ε') : ExceptT ε m α → ExceptT ε' m α := fun x =>
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ExceptT.mk <| Except.mapError f <$> x
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end ExceptT
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instance (m : Type u → Type v) (ε₁ : Type u) (ε₂ : Type u) [Monad m] [MonadExceptOf ε₁ m] : MonadExceptOf ε₁ (ExceptT ε₂ m) where
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throw e := ExceptT.mk <| throwThe ε₁ e
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tryCatch x handle := ExceptT.mk <| tryCatchThe ε₁ x handle
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instance (m : Type u → Type v) (ε : Type u) [Monad m] : MonadExceptOf ε (ExceptT ε m) where
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throw e := ExceptT.mk <| pure (Except.error e)
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tryCatch := ExceptT.tryCatch
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instance [Monad m] [Inhabited ε] : Inhabited (ExceptT ε m α) where
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default := throw arbitrary
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instance (ε) : MonadExceptOf ε (Except ε) where
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throw := Except.error
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tryCatch := Except.tryCatch
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namespace MonadExcept
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variable {ε : Type u} {m : Type v → Type w}
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/-- Alternative orelse operator that allows to select which exception should be used.
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The default is to use the first exception since the standard `orelse` uses the second. -/
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@[inline] def orelse' [MonadExcept ε m] {α : Type v} (t₁ t₂ : m α) (useFirstEx := true) : m α :=
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tryCatch t₁ fun e₁ => tryCatch t₂ fun e₂ => throw (if useFirstEx then e₁ else e₂)
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end MonadExcept
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@[inline] def observing {ε α : Type u} {m : Type u → Type v} [Monad m] [MonadExcept ε m] (x : m α) : m (Except ε α) :=
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tryCatch (do let a ← x; pure (Except.ok a)) (fun ex => pure (Except.error ex))
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instance (ε : Type u) (m : Type u → Type v) [Monad m] : MonadControl m (ExceptT ε m) where
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stM := Except ε
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liftWith f := liftM <| f fun x => x.run
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restoreM x := x
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class MonadFinally (m : Type u → Type v) where
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tryFinally' {α β} : m α → (Option α → m β) → m (α × β)
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export MonadFinally (tryFinally')
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/-- Execute `x` and then execute `finalizer` even if `x` threw an exception -/
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@[inline] def tryFinally {m : Type u → Type v} {α β : Type u} [MonadFinally m] [Functor m] (x : m α) (finalizer : m β) : m α :=
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let y := tryFinally' x (fun _ => finalizer)
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(·.1) <$> y
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instance Id.finally : MonadFinally Id where
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tryFinally' := fun x h =>
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let a := x
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let b := h (some x)
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pure (a, b)
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instance ExceptT.finally {m : Type u → Type v} {ε : Type u} [MonadFinally m] [Monad m] : MonadFinally (ExceptT ε m) where
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tryFinally' := fun x h => ExceptT.mk do
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let r ← tryFinally' x fun e? => match e? with
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| some (Except.ok a) => h (some a)
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| _ => h none
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match r with
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| (Except.ok a, Except.ok b) => pure (Except.ok (a, b))
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| (_, Except.error e) => pure (Except.error e) -- second error has precedence
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| (Except.error e, _) => pure (Except.error e)
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