Question

This is my FIRST haskell program! “wordCount” takes in a list of words and returns a tuple with with each case-insensitive word paired with its usage count. Any suggestions for improvement on either code readability or performance?

import List;
import Char;
uniqueCountIn ns xs = map (\x -> length (filter (==x) xs)) ns
nubl (xs) = nub (map (map toLower) xs) -- to lowercase
wordCount ws =  zip ns (uniqueCountIn ns ws)
   where ns = nubl ws

Answer 1

Congrats on your first program!

For cleanliness: lose the semicolons. Use the new hierarchical module names instead (Data.List, Data.Char). Add type signatures. As you get more comfortable with function composition, eta contract your function definitions (remove rightmost arguments). e.g.

nubl :: [String] -> [String]
nubl = nub . map (map toLower)

If you want to be really rigorous, use explicit import lists:

import Data.List (nub) 
import Data.Char (toLower)

For performance: use a Data.Map to store the associations instead of nub and filter. In particular, see fromListWith and toList. Using those functions you can simplify your implementation and improve performance at the same time.