Simple speller

speller.hs

import Debug.Trace

-- RULES

-- speller ["abacus"] -- > "a is for abacus"
-- speller [] -- > ""
-- speller ["apple", "banana", "coconut"] 
--  -- > "a is for apple, b is for banana, and c is for coconut"
-- speller ["whisky", "x-ray"]
--  -- > "w is for whisky, and x is for x-ray"
 

-- Creates the phrase for each word in the list entered
phrase :: [Char] -> [Char]
phrase word = [(word !! 0)] ++ " is for " ++ word


-- A bit ugly, is there a better way? 
-- This ensures that the position of [, and] are correct
position :: [Char] -> [Char] -> [Char]
position el acc = 
  if (acc /= "")  then (phrase el) ++ ", " ++ acc
                  else "and " ++ (phrase el)


-- Takes the array of strings entered and accumulates all the phrases
-- Matches 
--  1. Empty list 
--  2. Single phrase, no 'and' required
--  3. Every other case
display :: [[Char]] -> [Char]
display [] = ""
display (w:[]) = phrase w
display (w) =  foldr (\el acc -> position el acc) "" w  
  

-- Entry point
speller :: [[Char]] -> [Char]
speller words = display words