49 lines
1.4 KiB
Text
49 lines
1.4 KiB
Text
/-
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Copyright (c) 2016 Jared Roesch. 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
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-/
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prelude
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import init.category.monad
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namespace native
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inductive result (E : Type) (R : Type) : Type
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| err {} : E → result
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| ok {} : R → result
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def unwrap_or {E T : Type} : result E T → T → T
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| (result.err _) default := default
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| (result.ok t) _ := t
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def result.and_then {E T U : Type} : result E T → (T → result E U) → result E U
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| (result.err e) _ := result.err e
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| (result.ok t) f := f t
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instance result_monad (E : Type) : monad (result E) :=
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{pure := @result.ok E, bind := @result.and_then E}
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inductive resultT (M : Type → Type) (E : Type) (A : Type) : Type
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| run : M (result E A) → resultT
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section resultT
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variable {M : Type → Type}
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def resultT.pure [monad : monad M] {E A : Type} (x : A) : resultT M E A :=
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resultT.run $ return (result.ok x)
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def resultT.and_then [monad : monad M] {E A B : Type} : resultT M E A → (A → resultT M E B) → resultT M E B
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| (resultT.run action) f := resultT.run (do
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res_a ← action,
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-- a little ugly with this match
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match res_a with
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| result.err e := return (result.err e)
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| result.ok a := let (resultT.run actionB) := f a in actionB
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end)
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instance resultT_monad [m : monad M] (E : Type) : monad (resultT M E) :=
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{pure := @resultT.pure M m E, bind := @resultT.and_then M m E}
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end resultT
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end native
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