-- Curry with arithmetic constraints: {-# OPTIONS_CYMAKE -Wno-overlapping #-} import CLP.R import Test.Prop -- Example: -- Mortgage relationship between: -- p: Principal -- t: Life of loan in months -- ir: Fixed (but compounded) monthly interest rate -- r: Monthly repayment -- b: Outstanding balance at the end mortgage :: CFloat -> CFloat -> CFloat -> CFloat -> CFloat -> Bool mortgage p t ir r b | t > 0 & t <= 1 -- lifetime not more than 1 month? = b =:= p * (1 + t*ir) - t*r mortgage p t ir r b | t > 1 -- lifetime more than 1 month? = mortgage (p * (1+ir) - r) (t-1) ir r b -- Example: computing monthly payment for a mortgage: exPayment :: CFloat exPayment = let r free in mortgage 100000 180 0.01 r 0 &> r ex1 :: String ex1 = let r free in mortgage 100000 180 0.01 r 0 &> show r -- Compute time to amortize mortage (use ":set +first" here!): ex2 :: String ex2 = let time free in mortgage 100000 time 0.01 1400 0 &> show time -- Testing: testMG = always $ abs (exPayment - 1200.168) < 0.01