misc: add more scripts

misc/PhoneNo.hs

@@ -0,0 +1,19 @@
+{-# LANGUAGE LambdaCase #-}
+import Data.Char
+
+letters = \case
+  2 -> "ABC"
+  3 -> "DEF"
+  4 -> "GHI"
+  5 -> "JKL"
+  6 -> "MNO"
+  7 -> "PQRS"
+  8 -> "TUV"
+  9 -> "WXYZ"
+  _ -> []
+
+main :: IO ()
+main = interact $ unlines . possibleWords . digitsOf
+  where
+    possibleWords = mapM letters
+    digitsOf = map digitToInt . filter isDigit