Prelude> :t Data.List.mapAccumL
Data.List.mapAccumL :: (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])
I'm sure you can fill in the details :)
-- ryan
2008/10/8 Paul Keir
Hi,
I'd like to create a new list based on an original list, using information from a second (symbol) list. That second list should be updated as each element in the new list is added. I've been using map a lot, but that's not an option here, and I'm having trouble obtaining a good recursive structure for my function.
The minimal "fixpus" function below shows the problem. I have "sts" on both sides of the ":" list construct, but I'd like the second "sts" to be a version modified by the where (singular) function, "fixpu".
fixpus :: [ProgUnit] -> [ProgUnitSymbolTable] -> [ProgUnit] fixpus [] _ = [] fixpus (pu:pus) sts = fixpu pu sts : fixpus pus sts
where fixpu pu sts = pu
(Below) I tried making "fixpu" return a tuple, and then use "fst", "snd" and "let", but I think it looks strange. I know it's quite basic, but I'd like a strong foundation for what's likely to become a medium-scale project. Can anyone offer advice?
fixpus :: [ProgUnit] -> [ProgUnitSymbolTable] -> [ProgUnit] fixpus [] _ = [] fixpus (pu:pus) sts = let a = (fixpu pu sts) in fst a : fixpus pus (snd a)
where fixpu pu sts = (pu,sts ++ [("",[])])
Regards, Paul
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe