diff --git a/src/Lib.hs b/src/Lib.hs
index 2a548e4a6d6125d54bf9e07e3917686bcf5d9f55..0f0dc9817964d39dbf47ae3f0d342f479509d90f 100755
--- a/src/Lib.hs
+++ b/src/Lib.hs
@@ -20,7 +20,17 @@ handler person context =
   else
     return (Left "A person's age must be positive")
 
-netcashflow income outcome = zipWith (-) income outcome
-
+-- recursion
 power n 1 = n
 power n m = n * (power n (m-1))
+
+-- high order function
+netcashflow income outcome = zipWith (-) income outcome
+
+-- recursion
+powervalue m = 1 / (power (1 + interest) m)
+
+-- currying (variable nya bisa hilang)
+-- factorpresentvalue ns = map powervalue ns
+-- ns nya bisa dihilangkan
+factorpresentvalue = map powervalue