31 lines
852 B
Text
31 lines
852 B
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: Leonardo de Moura
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-/
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prelude
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import .basic
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import init.meta.tactic
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universes u v
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@[inline] def option_bind {α : Type u} {β : Type v} : option α → (α → option β) → option β
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| none b := none
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| (some a) b := b a
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instance : monad option :=
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{pure := @some, bind := @option_bind,
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id_map := λ α x, option.rec rfl (λ x, rfl) x,
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pure_bind := λ α β x f, rfl,
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bind_assoc := λ α β γ x f g, option.rec rfl (λ x, rfl) x}
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def option_orelse {α : Type u} : option α → option α → option α
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| (some a) o := some a
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| none (some a) := some a
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| none none := none
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instance : alternative option :=
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{ option.monad with
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failure := @none,
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orelse := @option_orelse }
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