42 lines
1.3 KiB
Text
42 lines
1.3 KiB
Text
/-
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Copyright (c) 2014 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: Leonardo de Moura
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Basic datatypes
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-/
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prelude
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import init.logic init.monad
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open decidable
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definition option_is_inhabited [instance] (A : Type) : inhabited (option A) :=
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inhabited.mk none
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definition option_has_decidable_eq [instance] {A : Type} [H : decidable_eq A] : ∀ o₁ o₂ : option A, decidable (o₁ = o₂)
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| none none := tt rfl
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| none (some v₂) := ff (λ H, option.no_confusion H)
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| (some v₁) none := ff (λ H, option.no_confusion H)
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| (some v₁) (some v₂) :=
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match H v₁ v₂ with
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| tt e := tt (congr_arg (@some A) e)
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| ff n := ff (λ H, option.no_confusion H (λ e, absurd e n))
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end
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namespace option
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inline protected definition fmap {A B : Type} (f : A → B) (e : option A) : option B :=
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option.cases_on e
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none
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(λ a, some (f a))
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inline protected definition bind {A B : Type} (a : option A) (b : A → option B) : option B :=
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option.cases_on a
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none
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(λ a, b a)
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inline protected definition return {A : Type} (a : A) : option A :=
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some a
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end option
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definition option.is_monad [instance] : monad option :=
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monad.mk @option.fmap @option.return @option.bind
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