Converting a string of characters into a list with a set layout in Haskell

Question

I've got the following function to enlarge, it takes a string such as "5a" and it outputs in a list, ie [('a',5)] . How could I change it so that it allows the input of more than just 1 pair, so if something like "5a5b" was input, the output would be [('a',5),('b',5)] ?

The current code that I have for this is here:

enlarge :: String -> [(Char,Int)]
enlarge [] = []
enlarge xs = [(a,b) | (b,a:_) <- reads xs]

The code above works and it will work for just one pair, ie if "5a" is input, it will output [('a',5)] . However, I'd like to change it so that it will allow more than just one pair, ie if "5a3b" is input, the output should be [('a',5),('b',3)] . Currently, it only takes into consideration the first 2 parts of the string.

My attempt at doing this is here:

enlarge xs = [((a,b),ts) | ((b,a),ts) <- reads xs, reads ts]

And what i'm trying to do here, is first get the pair for the first two characters, and then read any more characters and then do the same to those.

Answer 1

I wrote a recursive code for your request.

enlarge :: String -> [(Char,Int)]
enlarge [] = []
enlarge (x:y:ls) = [(y,digitToInt x)] ++ enlarge ls

Here, the code assumes that the input length is even. And used digitToInt to convert the Char to Int.

Answer 2

We need more input-output examples. For example what should happen to "12z" ? Also it is not really clear what reads means. But I think you want this

[(c, read i :: Int) | [i, c] <- chunksOf 2 xs]

Don't forget to import chunksOf , which can be found in Data.List.Split .