Add Haskell subSequences (#121)

* Add Haskell Sequence

* Add type signature for the function

* Add aim of sequence.hs program

Co-authored-by: Arsenic <54987647+Arsenic-ATG@users.noreply.github.com>

strings/README.md

@@ -34,5 +34,6 @@
 
 ### Haskell
 
-1. [Palin Check](haskell/palindrome.hs)
+1. [Palindrome Check](haskell/palindrome.hs)
+2. [All subsequences](haskell/sequence.hs)
 

strings/haskell/sequence.hs

@@ -0,0 +1,8 @@
+-- program to generate all subsequences of a sequence
+
+import Control.Monad (filterM)
+
+findSubSequences :: String -> [String]
+findSubSequences = filterM $ const [True, False] 
+
+main = traverse print $ findSubSequences "abc"