tests: sqrt example from SICP

1 files changed, 37 insertions, 0 deletions

diff --git a/test/square-root.scm b/test/square-root.scm
new file mode 100644
index 0000000..4c2c1cf
--- /dev/null
+++ b/test/square-root.scm
@@ -0,0 +1,37 @@
+; see: https://mitpress.mit.edu/sicp/chapter1/node9.html
+
+(define square
+  (lambda (x)
+    (* x x)))
+
+(define average
+  (lambda (x y)
+    (/ (+ x y) 2)))
+
+(define improve
+  (lambda (guess x)
+    (average guess (/ x guess))))
+
+(define good-enough?
+  (lambda (guess x)
+    (< (abs (- x (square guess)))
+       0.001)))
+
+(define sqrt-iter
+  (lambda (guess x)
+    (if (good-enough? guess x)
+      guess
+      (sqrt-iter (improve guess x) x))))
+
+(define test-sqrt
+  (lambda (x)
+    (sqrt-iter 1.0 x)))
+
+(test-sqrt 9)
+;  => 3.00009155413138
+(test-sqrt (+ 100 37))
+;  => 11.704699917758145
+(test-sqrt (+ (test-sqrt 2) (test-sqrt 3)))
+;  => 1.7739279023207892
+(square (test-sqrt 1000))
+;  => 1000.000369924366