works fine in guile. Not that well in racket for 100000 iterations.

diff --git a/src/sicp/ex3_5.rkt b/src/sicp/ex3_5.rkt
new file mode 100644 (file)
index 0000000..c93f777
--- /dev/null
+++ b/src/sicp/ex3_5.rkt
@@ -0,0 +1,35 @@
+#lang racket
+
+(define (monte-carlo trials experiment)
+  (define (iter trials-remaining trials-passed)
+    (cond 
+      ((= trials-remaining 0) (/ trials-passed trials))
+      ((experiment) (iter (- trials-remaining 1) (+ trials-passed 1)))
+      (else (iter (- trials-remaining 1) trials-passed))))
+  (iter trials 0))
+
+(define (square x)
+  (* x x))
+
+(define (random-in-range low high)
+  (let ((range (- high low)))
+    (+ low (random range))))
+
+(define (P x y)
+  (define (inside-circle? radius centre-x centre-y)
+    (<= (+ (square (- x centre-x))
+           (square (- y centre-y)))
+        (square radius)))
+  (inside-circle? 1.0 0 0))
+
+(define (estimate-integral P x1 x2 y1 y2 trials)
+  (define (in-region)
+    (let ((x (random-in-range x1 x2))
+          (y (random-in-range y1 y2)))
+      (P x y)))
+  (define (rectangle-area x1 x2 y1 y2)
+    (* (- x2 x1) (- y2 y1)))
+  
+  (* (monte-carlo trials in-region) 
+     (rectangle-area x1 x2 y1 y2)))
+    
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