Haskell: Scan Through a List and Apply A Different Function for Each Element

Question

I need to scan through a document and accumulate the output of different functions for each string in the file. The function run on any given line of the file depends on what i

Answer 1

If you have only 2 alternatives, using Either might be a good idea. In that case combine your functions, map the list, and use lefts and rights to get the results:

import Data.Either

-- first sample function, returning String
f1 x = show $ x `div` 2

-- second sample function, returning Int
f2 x = 3*x+1

-- combined function returning Either String Int
hotpo x = if even x then Left (f1 x) else Right (f2 x)

xs = map hotpo [1..10] 
-- [Right 4,Left "1",Right 10,Left "2",Right 16,Left "3",Right 22,Left "4",Right 28,Left "5"]

lefts xs 
-- ["1","2","3","4","5"]

rights xs
-- [4,10,16,22,28]