[pure-lang-svn] SF.net SVN: pure-lang:[694] pure/trunk/examples/hello.pure

[<ag...@us...>]

Revision: 694
          http://pure-lang.svn.sourceforge.net/pure-lang/?rev=694&view=rev
Author:   agraef
Date:     2008-09-04 00:45:30 +0000 (Thu, 04 Sep 2008)

Log Message:
-----------
Add stream example.

Modified Paths:
--------------
    pure/trunk/examples/hello.pure

Modified: pure/trunk/examples/hello.pure
===================================================================
--- pure/trunk/examples/hello.pure	2008-09-03 22:02:24 UTC (rev 693)
+++ pure/trunk/examples/hello.pure	2008-09-04 00:45:30 UTC (rev 694)
@@ -166,6 +166,26 @@
 
 primes 100;
 
+/* Using streams (lazy lists), we can also compute the infinite list of *all*
+   prime numbers. */
+
+all_primes	= sieve (2..inf) with
+  sieve []	= [];
+  sieve (p:qs)	= p : sieve [q; q = qs; q mod p] &;
+end;
+
+// Assign this to a variable, so we can take advantage of memoization.
+let P = all_primes;
+
+// The primes <=100, this is the same as primes 100.
+let P1 = list $ takewhile (\x->x<=100) P; P1;
+
+// The first 30 primes.
+let P2 = list $ take 30 P; P2;
+
+// The 299th prime.
+P!299;
+
 /* The classical n queens problem: Compute all placements of n queens on an
    n x n board so that no two queens hold each other in check. This algorithm
    demonstrates how you can use list comprehensions to organize backtracking


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