23 lines
779 B
Text
23 lines
779 B
Text
/-
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Copyright (c) 2016 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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Author: Leonardo de Moura
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-/
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prelude
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import init.logic init.applicative
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universe variables u v
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class alternative (F : Type u → Type v) extends applicative F : Type (max u+1 v) :=
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(failure : Π {A : Type u}, F A)
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(orelse : Π {A : Type u}, F A → F A → F A)
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@[inline] def failure {F : Type u → Type v} [alternative F] {A : Type u} : F A :=
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alternative.failure F
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@[inline] def orelse {F : Type u → Type v} [alternative F] {A : Type u} : F A → F A → F A :=
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alternative.orelse
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infixr ` <|> `:2 := orelse
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@[inline] def guard {F : Type → Type v} [alternative F] (P : Prop) [decidable P] : F unit :=
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if P then pure () else failure
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