56 lines
1.6 KiB
Text
56 lines
1.6 KiB
Text
/-
|
|
Copyright (c) 2016 Microsoft Corporation. All rights reserved.
|
|
Released under Apache 2.0 license as described in the file LICENSE.
|
|
Authors: Leonardo de Moura
|
|
-/
|
|
prelude
|
|
import init.monad init.meta.format
|
|
/-
|
|
Remark: we use a function that produces a format object as the exception information.
|
|
Motivation: the formatting object may be big, and we may create it on demand.
|
|
-/
|
|
inductive exceptional (A : Type)
|
|
| success : A → exceptional
|
|
| exception : (options → format) → exceptional
|
|
|
|
section
|
|
open exceptional
|
|
variables {A : Type}
|
|
variables [has_to_string A]
|
|
|
|
protected meta_definition exceptional.to_string : exceptional A → string
|
|
| (success a) := to_string a
|
|
| (exception .A e) := "Exception: " ++ to_string (e options.mk)
|
|
|
|
attribute [instance]
|
|
protected meta_definition exceptional.has_to_string : has_to_string (exceptional A) :=
|
|
has_to_string.mk exceptional.to_string
|
|
end
|
|
|
|
namespace exceptional
|
|
variables {A B : Type}
|
|
|
|
attribute [inline]
|
|
protected meta_definition fmap (f : A → B) (e : exceptional A) : exceptional B :=
|
|
exceptional.cases_on e
|
|
(λ a, success (f a))
|
|
(λ f, exception B f)
|
|
|
|
attribute [inline]
|
|
protected meta_definition bind (e₁ : exceptional A) (e₂ : A → exceptional B) : exceptional B :=
|
|
exceptional.cases_on e₁
|
|
(λ a, e₂ a)
|
|
(λ f, exception B f)
|
|
|
|
attribute [inline]
|
|
protected meta_definition return (a : A) : exceptional A :=
|
|
success a
|
|
|
|
attribute [inline]
|
|
meta_definition fail (f : format) : exceptional A :=
|
|
exception A (λ u, f)
|
|
end exceptional
|
|
|
|
attribute [instance]
|
|
meta_definition exceptional.is_monad : monad exceptional :=
|
|
monad.mk @exceptional.fmap @exceptional.return @exceptional.bind
|