From 4588333f1329bc1f217688588aeea628357e4c34 Mon Sep 17 00:00:00 2001
From: Ari Angga Nugraha <ari.angga@ui.ac.id>
Date: Sun, 27 Dec 2020 14:17:15 +0700
Subject: [PATCH] implement type system
---
src/NetPresentValue.hs | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/src/NetPresentValue.hs b/src/NetPresentValue.hs
index af73ac8..735ed01 100644
--- a/src/NetPresentValue.hs
+++ b/src/NetPresentValue.hs
@@ -29,25 +29,29 @@ calculateNetPresentValue :: InputNetPresentValue -> Double
calculateNetPresentValue inputNetPresentValue = netPresentValue inputNetPresentValue
-- high order function
+netPresentValue :: InputNetPresentValue -> Double
netPresentValue inputNetPresentValue = foldl (+) 0 pv
where
pv = presentValue inputNetPresentValue
-- high order function
+presentValue :: InputNetPresentValue -> [Double]
presentValue inputNetPresentValue = zipWith (*) (netcashflow income outcome) (factorpresentvalue (project_interest inputNetPresentValue))
where
income = [income_1 inputNetPresentValue, income_2 inputNetPresentValue, income_3 inputNetPresentValue, income_4 inputNetPresentValue, income_5 inputNetPresentValue]
outcome = [outcome_1 inputNetPresentValue, outcome_2 inputNetPresentValue, outcome_3 inputNetPresentValue, outcome_4 inputNetPresentValue, outcome_5 inputNetPresentValue]
-- currying
+-- partial evaluation
+netcashflow :: [Double] -> [Double] -> [Double]
netcashflow = zipWith (-)
--- recursion
-power n 1 = n
-power n m = n * (power n (m-1))
-
--- recursion
-powervalue interest n = 1 / (power (1 + interest) n)
+-- pure function
+powervalue :: Floating a => a -> a -> a
+powervalue interest n = 1 / ((1 + interest)**n)
-- high order function
+-- anonymous function
+-- polymorphic
+factorpresentvalue :: (Floating b, Enum b) => b -> [b]
factorpresentvalue interest = map (\x -> powervalue interest x) [1..5]
--
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