{- |

Module : $Header$

Description : supply a default morphism for a given signature type

Copyright : (c) C. Maeder, and Uni Bremen 2002-2006

License : similar to LGPL, see HetCATS/LICENSE.txt or LIZENZ.txt

Maintainer : Christian.Maeder@dfki.de

Stability : provisional

Portability : portable

Supply a default morphism for a given signature type

-}

-- due to functional deps the instance for Logic.Category cannot be supplied

module Common.DefaultMorphism where

import Common.Keywords

import Common.Doc

import Common.DocUtils

data DefaultMorphism sign = MkMorphism sign sign deriving (Show, Eq)

instance Pretty a => Pretty (DefaultMorphism a) where

pretty = printDefaultMorphism pretty

printDefaultMorphism :: (a -> Doc) -> DefaultMorphism a -> Doc

printDefaultMorphism fA (MkMorphism s t) =

specBraces (fA s) $+$ (text mapsTo) <+> specBraces (fA t)

domOfDefaultMorphism, codOfDefaultMorphism :: DefaultMorphism sign -> sign

domOfDefaultMorphism (MkMorphism s _) = s

codOfDefaultMorphism (MkMorphism _ s) = s

ideOfDefaultMorphism :: sign -> DefaultMorphism sign

ideOfDefaultMorphism s = MkMorphism s s

compOfDefaultMorphism :: (Monad m, Eq sign) => DefaultMorphism sign

-> DefaultMorphism sign -> m (DefaultMorphism sign)

compOfDefaultMorphism (MkMorphism s1 s) (MkMorphism s2 s3) =

if s == s2 then return $ MkMorphism s1 s3 else

fail "intermediate signatures are different"

legalDefaultMorphism :: (sign -> Bool) -> DefaultMorphism sign -> Bool

legalDefaultMorphism legalSign (MkMorphism s t) =

legalSign s && legalSign t

defaultInclusion :: (Monad m) => (sign -> sign -> Bool) -> sign -> sign

-> m (DefaultMorphism sign)

defaultInclusion isSubSig s1 s2 =

if isSubSig s1 s2 then return $ MkMorphism s1 s2 else

fail "non subsignatures for inclusion"