A lisp function to compute compound interest and unit tests

lisp/compound-test.lisp

@@ -0,0 +1,33 @@
+(load "unit-test.lisp")
+(load "compound.lisp")
+
+(unit
+  (list
+
+    (defun many-years-with-no-interest-rate ()
+      (eq (compound 100000 0 10) 100000)
+    )
+
+    (defun no-years-with-positive-interest-rate ()
+      (eq (compound 100000 10 0) 100000)
+    )
+
+    (defun one-year-with-positive-interest-rate ()
+      (eq (compound 100000 5 1) 105000)
+    )
+
+    (defun two-years-with-positive-interest-rate ()
+      (eq (compound 100000 5 2) 110250)
+    )
+
+    (defun three-years-with-positive-interest-rate ()
+      (eq (compound 100000 5 3) 115763)
+    )
+
+    (defun four-years-with-positive-interest-rate ()
+      (eq (compound 100000 5 4) 121551)
+    )
+
+  )
+)
+

lisp/compound.lisp

@@ -0,0 +1,14 @@
+(defun compound (principal interest-rate years)
+  (cond
+    ((= years 0) principal)
+    (t (let ( (previous-principal (compound principal interest-rate (- years 1))) )
+            (+ previous-principal
+               (/ (+ (* previous-principal
+                        interest-rate)
+                     50)
+                  100)
+            )
+       )
+    )
+  )
+)

lisp/unit-test.lisp

@@ -1,7 +1,7 @@
 (defun run-unit-test (unit-test)
   (cond
-    ((funcall unit-test) (print (cons (symbol-function unit-test) T)) T)
-    (T (print (cons (symbol-function unit-test) 'F)) NIL)
+    ((funcall unit-test) (print (cons T unit-test)) T)
+    (T (print (cons 'F unit-test)) NIL)
   )
 )