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Add function to interest-compounder

This commit is contained in:
Mike Cifelli 2017-03-07 11:37:27 -05:00
parent 5f10396af8
commit e9fead08c2
2 changed files with 69 additions and 36 deletions
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87
lisp/finance/interest-compounder-test.lisp
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@ -7,74 +7,97 @@
(defun principal-initialized () (defun principal-initialized ()
(setf compounder (interest-compounder 1000 0)) (setf compounder (interest-compounder 1000 0))
(assert= 1000 (funcall compounder :get-principal))) (assert= 1000 (call compounder :get-principal)))
(defun interest-rate-initialized () (defun interest-rate-initialized ()
(setf compounder (interest-compounder 0 10)) (setf compounder (interest-compounder 0 10))
(assert= 10 (funcall compounder :get-interest-rate))) (assert= 10 (call compounder :get-interest-rate)))
(defun many-years-with-no-interest-rate () (defun many-years-with-no-interest-rate ()
(setf compounder (interest-compounder 1000 0)) (setf compounder (interest-compounder 1000 0))
(funcall compounder :move-forward-years 83) (call compounder :move-forward-years 83)
(assert= 1000 (funcall compounder :get-principal))) (assert= 1000 (call compounder :get-principal)))
(defun no-years-with-positive-interest-rate () (defun no-years-with-positive-interest-rate ()
(setf compounder (interest-compounder 1000 10)) (setf compounder (interest-compounder 1000 10))
(assert= 1000 (funcall compounder :get-principal))) (assert= 1000 (call compounder :get-principal)))
(defun one-year-with-positive-interest-rate () (defun one-year-with-positive-interest-rate ()
(setf compounder (interest-compounder 100000 5)) (setf compounder (interest-compounder 100000 5))
(funcall compounder :move-forward-one-year) (call compounder :move-forward-years 1)
(assert= 105000 (funcall compounder :get-principal))) (assert= 105000 (call compounder :get-principal)))
(defun two-years-with-positive-interest-rate () (defun two-years-with-positive-interest-rate ()
(setf compounder (interest-compounder 100000 5)) (setf compounder (interest-compounder 100000 5))
(funcall compounder :move-forward-one-year) (call compounder :move-forward-years 2)
(funcall compounder :move-forward-one-year) (assert= 110250 (call compounder :get-principal)))
(assert= 110250 (funcall compounder :get-principal)))
(defun three-years-with-positive-interest-rate () (defun three-years-with-positive-interest-rate ()
(setf compounder (interest-compounder 100000 5)) (setf compounder (interest-compounder 100000 5))
(funcall compounder :move-forward-years 3) (call compounder :move-forward-years 3)
(assert= 115763 (funcall compounder :get-principal))) (assert= 115763 (call compounder :get-principal)))
(defun four-years-with-positive-interest-rate () (defun four-years-with-positive-interest-rate ()
(setf compounder (interest-compounder 100000 5)) (setf compounder (interest-compounder 100000 5))
(funcall compounder :move-forward-years 4) (call compounder :move-forward-years 4)
(assert= 121551 (funcall compounder :get-principal))) (assert= 121551 (call compounder :get-principal)))
(defun one-year-with-negative-interest-rate () (defun one-year-with-negative-interest-rate ()
(setf compounder (interest-compounder 100000 -5)) (setf compounder (interest-compounder 100000 -5))
(funcall compounder :move-forward-years 1) (call compounder :move-forward-years 1)
(assert= 95000 (funcall compounder :get-principal))) (assert= 95000 (call compounder :get-principal)))
(defun two-years-with-negative-interest-rate () (defun two-years-with-negative-interest-rate ()
(setf compounder (interest-compounder 100000 -5)) (setf compounder (interest-compounder 100000 -5))
(funcall compounder :move-forward-years 2) (call compounder :move-forward-years 2)
(assert= 90250 (funcall compounder :get-principal))) (assert= 90250 (call compounder :get-principal)))
(defun three-years-with-negative-interest-rate () (defun three-years-with-negative-interest-rate ()
(setf compounder (interest-compounder 100000 -5)) (setf compounder (interest-compounder 100000 -5))
(funcall compounder :move-forward-years 3) (call compounder :move-forward-years 3)
(assert= 85737 (funcall compounder :get-principal))) (assert= 85737 (call compounder :get-principal)))
(defun four-years-with-negative-interest-rate () (defun four-years-with-negative-interest-rate ()
(setf compounder (interest-compounder 100000 -5)) (setf compounder (interest-compounder 100000 -5))
(funcall compounder :move-forward-years 4) (call compounder :move-forward-years 4)
(assert= 81450 (funcall compounder :get-principal))) (assert= 81450 (call compounder :get-principal)))
(defun negative-number-of-years-does-nothing () (defun negative-number-of-years-does-nothing ()
(setf compounder (interest-compounder 100000 5)) (setf compounder (interest-compounder 100000 5))
(funcall compounder :move-forward-years -4) (call compounder :move-forward-years -4)
(assert= 100000 (funcall compounder :get-principal)) (assert= 100000 (call compounder :get-principal))
(funcall compounder :move-forward-years 1) (call compounder :move-forward-years 1)
(funcall compounder :move-forward-years -4) (call compounder :move-forward-years -4)
(assert= 105000 (funcall compounder :get-principal))) (assert= 105000 (call compounder :get-principal)))
(defun zero-number-of-years-does-nothing () (defun zero-number-of-years-does-nothing ()
(setf compounder (interest-compounder 100000 5)) (setf compounder (interest-compounder 100000 5))
(funcall compounder :move-forward-years 0) (call compounder :move-forward-years 0)
(assert= 100000 (funcall compounder :get-principal)) (assert= 100000 (call compounder :get-principal))
(funcall compounder :move-forward-years 1) (call compounder :move-forward-years 1)
(funcall compounder :move-forward-years 0) (call compounder :move-forward-years 0)
(assert= 105000 (funcall compounder :get-principal)))))) (assert= 105000 (call compounder :get-principal)))
(defun variable-interest-rate ()
(setf compounder (interest-compounder 100000 5))
(call compounder :move-forward-years 2)
(call compounder :set-interest-rate 10)
(call compounder :move-forward-years 2)
(assert= 133403 (call compounder :get-principal)))
(defun years-are-updated ()
(setf compounder (interest-compounder 100000 5))
(call compounder :move-forward-years 27)
(assert= 27 (call compounder :get-years-passed)))
(defun negative-number-of-years-does-not-update-years ()
(setf compounder (interest-compounder 100000 5))
(call compounder :move-forward-years 27)
(call compounder :move-forward-years -2)
(assert= 27 (call compounder :get-years-passed)))
(defun zero-number-of-years-does-not-update-years ()
(setf compounder (interest-compounder 100000 5))
(call compounder :move-forward-years 27)
(call compounder :move-forward-years 0)
(assert= 27 (call compounder :get-years-passed))))))

18
lisp/finance/interest-compounder.lisp
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@ -3,12 +3,17 @@
(defun interest-compounder (initial-principal initial-interest-rate) (defun interest-compounder (initial-principal initial-interest-rate)
(let ((private) (public) (let ((private) (public)
(principal initial-principal) (principal initial-principal)
(interest-rate initial-interest-rate)) (interest-rate initial-interest-rate)
(years-passed 0))
(setf private (setf private
(eval (eval
(dlambda (dlambda
(:add-years (years)
(if (> years 0)
(setf years-passed (+ years-passed years))))
(:percent-of-number (n percentage) (:percent-of-number (n percentage)
(if (> percentage 0) (if (> percentage 0)
(/ (+ (* n percentage) 50) 100) (/ (+ (* n percentage) 50) 100)
@ -26,14 +31,19 @@
(eval (eval
(dlambda (dlambda
(:get-years-passed ()
years-passed)
(:get-principal () (:get-principal ()
principal) principal)
(:get-interest-rate () (:get-interest-rate ()
interest-rate) interest-rate)
(:move-forward-one-year () (:set-interest-rate (new-interest-rate)
(call private :compound-interest 1)) (setf interest-rate new-interest-rate))
(:move-forward-years (years) (:move-forward-years (years)
(call private :compound-interest years))))))) (progn
(call private :add-years years)
(call private :compound-interest years))))))))