X-Git-Url: https://git.rkrishnan.org/?p=sicp.git;a=blobdiff_plain;f=src%2Fsicp%2Fex4_36.rkt;fp=src%2Fsicp%2Fex4_36.rkt;h=5c9ec2d5fecb5c62d5248fe1f7fbe640cb195e27;hp=0000000000000000000000000000000000000000;hb=16ffd75b36a5dbfbda3da703c2732f8f49208c11;hpb=ef9bb63c4d3fa21f9964c3a5e612bfc519406744

diff --git a/src/sicp/ex4_36.rkt b/src/sicp/ex4_36.rkt
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+++ b/src/sicp/ex4_36.rkt
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+#lang racket
+
+(require "amb-eli.rkt")
+
+(define (an-integer-starting-from n)
+  (amb n (an-integer-starting-from (+ n 1))))
+
+(define (an-integer-between low high)
+  (assert (< low high))
+  (amb low (an-integer-between (+ low 1) high)))
+
+#|
+
+If we replace an-integer-between with an-integer-starting-from, then
+the k grows too high to invalid ranges and never stops. The way to accomplish
+correct values is to restrict i, j and k to valid ranges.
+
+|#
+
+;; using euclid's formula
+;; http://en.wikipedia.org/wiki/Pythagorean_triple#Generating_a_triple
+(define (pythagorean-triples)
+  (let [(n (an-integer-starting-from 1))]
+    (let [(m (an-integer-starting-from n))]
+      (assert (> m n))
+      (list (- (sqr m) (sqr n))
+            (* 2 m n)
+            (+ (sqr m) (sqr n))))))
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