Ibid.hs

-- Build this with "ghc ibid.hs"
-- Test it with "./ibid"

-- Import some list functions
import Data.List

-- Some refs to test on
refs = ["book1","book2","ibid","ibid","paper1","ibid","paper2","book3"]

-- Code close to what John wrote that will work in ghci
addRef curr_ref (last_ref,refList) =
    if curr_ref == "ibid" then
        (last_ref, last_ref:refList)
    else
        (curr_ref, curr_ref:refList)

flushIBID refs = reverse (snd(foldr addRef ("unknown",[]) (reverse refs)))

-- Function to try out an implementation
tryIt name func input = do
    putStrLn $ "Trying out function " ++ name
    putStrLn $ "  input = " ++ (show input)
    putStrLn $ "  output = " ++ (show (func input)) ++ "\n"

-- Try it out
tryIBID = tryIt "flushIBID" flushIBID refs

-- Alternate implementation (also ghci compatible)
expandCurrRef prev_ref cur_ref = if cur_ref == "ibid" then prev_ref else cur_ref
flushIBID2 refs = scanl1 expandCurrRef refs

-- Try it out
tryIBID2 = tryIt "flushIBID2" flushIBID2 refs

-- Inverse transformation (add IBIDs)
ibidCurrRef prev_ref cur_ref = if prev_ref == cur_ref then (prev_ref,"ibid") else (cur_ref,cur_ref)
addIBID refs = snd (mapAccumL ibidCurrRef "unknown" refs)

-- Try it out
tryAddIBID = tryIt "addIBID" addIBID (flushIBID refs)

main = do
    tryIBID
    tryIBID2
    tryAddIBID