write a functional program to list phone letters permutations without a single bracket
The aim of this puzzle is to list all the possible words that you can write using an old phone keypad like this one :
using intuitive (and not repetitive) input : only one digit per character.
Example : TEST would be written using the number 8378.
The achievement does not require to filter the list with a dictionary. We only need to list all the possibilities in this puzzle.
Good luck.