Question

Hey I’m just revising for my functional programming exam coming up on friday and I’m just working through exercises given by our lecturer. I’ve come across one which I neep a bit of help on:

6. a) Write a function that zips a given list xs with every list in a list yss of lists. Use partial
applications and lambda expressions to the greatest extent possible in defining your function.
b) Write a function that zips every list in a list yss of lists with a given list xs. Use partial
applications and lambda expressions to the greatest extent possible in defining your function.
The difference between your solutions to part a) and part b) of this problem illustrates that partially
applied functions must take their arguments in the correct order.

What I have at the moment for (a) is :

zipAll = (\xs (ys:yss) -> [(zip xs ys)] ++ zipAll xs yss)

It’s non-exaustive I know but could anyone give me some pointers?

Answer 1

Its fine, I worked it out:

zipList :: [a] -> [[b]] -> [[(a,b)]]
zipList = \xs yss -> c xs yss
                        where
                                c xs [] = []
                                c xs (ys:yss) = zip xs ys :zipList xs yss

Just wish I hadn’t posted this now 😛