Thanks Stuart, Ovidiu. Yes, partially applied functions is the way. Mike

On 18 Dec 2017, at 16:00, Stuart Dootson wrote:

Something like the code below - populate a list with partially applied functions, then use foldl to apply the functions in turn to the input list?

v :: Int -> [a] -> [a] v = drop

w :: Int -> Int -> [a] -> [a] w keep reject = (take keep).(drop reject)

-- Apply the list of functions (in turn) to the list, yielding a list apply_ops :: [ [a] -> [a] ] -> [a] -> [a] apply_ops fns l = foldl (flip ($)) l fns

-- Partially apply functions with non-list arguments to get list of functions of type [a] -> [a] ops :: [ [a] -> [a] ] ops = [v 3, w 2 1]

-- result = (w 2 1) ((v 3)[1,2,3,4,5,6,7,8]) -- = w [4,5,6,7,8] -- = [5,6] result :: [Int] result = apply_ops ops [1,2,3,4,5,6,7,8]

main = do print result

On 17 December 2017 at 09:32, mike h mailto:mike_k_houghton@yahoo.co.uk> wrote: Hi,

I have a number of functions like these:

v :: Int -> [a] -> [a] w :: Int -> Int -> [a] -> [a] x :: a -> a -> [a] -> [a]

y :: a -> b ->… <other args>... -> [a] -> [a] z… etc.

where there are any number of args of different types but the last two are common to all the functions i.e. they all have [a] -> [a]

What I’m trying to do is build a collection (ordered) of such functions and then apply each in turn to a [a] to get the final [a]. What would be the best approach to this?

Thanks

Mike _______________________________________________ Beginners mailing list Beginners@haskell.org mailto:Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners

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