{- |

Module : $Header$

Description : compute the differences of two unshared ATerms

Copyright : (c) Klaus Luettich, Uni Bremen 2005

License : GPLv2 or higher, see LICENSE.txt

Maintainer : Christian.Maeder@dfki.de

Stability : provisional

Portability : non-portable (imports ATerm.Unshared)

Provides functions that calculate differences in unshared 'ATerm's.

-}

module ATerm.Diff (atDiff) where

import ATerm.Unshared

import Data.List

{- | all diferences between both terms are replaced by appropiate

placeholders (in @\<\>@) and the differing terms are added to the

list of ATerm as arguments to the function symbol @diff@. -}

--

{- /Note:

this function ignores annotions and the resulting ATerm does not

contain any annotation!/ -}

atDiff :: ATerm -> ATerm -> (ATerm, [ATerm])

atDiff a1@(AAppl s1 atl1 _) a2@(AAppl s2 atl2 _)

| s1 == s2 && atl1 == atl2 = (AAppl s1 atl1 [], [])

| s1 == s2 &&

length atl1 == length atl2 =

case atDiffL atl1 atl2 of

(diffs, atl) -> (AAppl s1 atl [], diffs)

| otherwise = (AAppl "<diff-appls>" [] [], [AAppl "diff" [a1, a2] []])

atDiff a1@(AInt i1 _) a2@(AInt i2 _)

| i1 == i2 = (AInt i1 [], [])

| otherwise = (AAppl "<diff-int>" [] [], [AAppl "diff" [a1, a2] []])

atDiff a1@(AList l1 _) a2@(AList l2 _)

| l1 == l2 = (AList l1 [], [])

| length l1 == length l2 =

case atDiffL l1 l2 of

(diffs, atl) -> (AList atl [], diffs)

| otherwise = (AList [AAppl "<diff-lists>" [] []] [],

[AAppl "diff" [a1, a2] []])

atDiff a1 a2 = (AAppl "<diff-types>" [] [], [AAppl "diff" [a1, a2] []])

atDiffL :: [ATerm] -> [ATerm] -> ([ATerm], [ATerm])

atDiffL atl1 atl2 =

mapAccumL (\ acc (ia1, ia2) ->

case atDiff ia1 ia2 of

(at, diffs) -> (acc ++ diffs, at)) [] (zip atl1 atl2)