One question I have is whether I can eliminate points in the above definition of blowup, and write something like
blowup = (++) . (blowup . allButLast, lastToTheLength)
thinking of (++) as a function String x String -> String.
Actually (++) is of type String -> String -> String. When you want something of the type you mean (you normally write that as (String, String) -> String in Haskell, then you can use (uncurry (++)). Additionally, you can't combine the functions (blowup . allButLast) and lastToTheLength into a function that returns a pair like you seem to attempt. You need a function like the following for that: comma :: (a -> b) -> (a -> c) -> a -> (b,c) comma f g x = (f x, g x) Then you could say: blowup = (uncurry (++)) . comma (blowup . allButLast) lastToTheLength Ignore this if you haven't read about Applicative or type classes yet, but using the Applicative instance for arrow types (->) a, you can also write comma = liftA2 (,) or blowup = (uncurry (++)) . liftA2 (,) (blowup . allButLast) lastToTheLength
Also, I can't figure out whether it is possible to get a shorter solution using fold. I have tried Hlint on my file, but it gave no suggestions.
I am sure there are better ways, and would like some pointers and any general suggestions for improvement.
By the way, shorter is not always better. Trying to recognize abstraction patterns in your code is never a bad thing though. Dominique