-- Alloy.
-- Copyright (c) 2008-2009, University of Kent.
-- All rights reserved.
-- 
-- Redistribution and use in source and binary forms, with or without
-- modification, are permitted provided that the following conditions are
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--
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--  * Redistributions in binary form must reproduce the above copyright
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--
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-- | A module providing an 'Alloy' instance in terms of 'AlloyA'.
--
-- The contents of this module appear blank because it contains only class instances.
--  The 'Alloy' and 'AlloyA' class instances have nearly identical definitions
-- for any given type, and running 'AlloyA' with an identity functor\/monad has
-- the same behaviour as the pure class.  Therefore, it is possible to define
-- a single 'Alloy' instance in terms of 'AlloyA'.  That is what this module does.
--
-- To use this module, you should generate only 'AlloyA' instances with the
-- "Data.Generics.Alloy.GenInstances" module, and import this module.  If you
-- import this alongside any other 'Alloy' instances you'll have incoherent
-- instances.  Alternatively, you can generate only 'AlloyARoute' instances and
-- use this module along with "Data.Generics.Alloy.EffectProxy".
module Data.Generics.Alloy.PureProxy () where

import Control.Monad.Identity

import Data.Generics.Alloy

instance (AlloyA t mo mo', ConvertOpsToIdentity o mo, ConvertOpsToIdentity o' mo') => Alloy t o o' where
  transform o o' t = runIdentity (transformM (convertOpsToIdentity o) (convertOpsToIdentity o') t)

-- {{{ Various type-level programming ops conversions:

-- | A helper class to convert non-monadic transformations into monadic ones in
-- the Identity monad.
class ConvertOpsToIdentity o o' | o -> o' where
  convertOpsToIdentity :: o -> o' Identity

instance ConvertOpsToIdentity BaseOp BaseOpA where
  convertOpsToIdentity = const baseOpA

instance ConvertOpsToIdentity r r' => ConvertOpsToIdentity (a :- r) (a :-* r') where
  convertOpsToIdentity (f :- r) = (return . f) :-* (convertOpsToIdentity r)


-- }}}