adding binomial coefficient example

Author: L. Grondin

best-of-rosettacode/binomial-coefficient.pl

@@ -0,0 +1,31 @@
+=begin pod
+
+=head1 Binomial Coefficient
+
+Number of ways to choose P objects among N.  It's also the coefficient of the
+monome of degree P in the expansion of (1 + X)^N, thus the name.
+
+
+     N       (N-P+1)*(N-P)*...*N
+   (   ) = ∑ -------------------
+     P         1*2*...*P
+
+
+=head1 More
+
+L<http://rosettacode.org/wiki/Evaluate_binomial_coefficients#Perl_6>
+
+=head1 Notable features used
+
+=item infix sub definition
+=item reduction meta-operator
+=item self-declared parameters
+=item range operator with first value excluded
+=item Zip metaoperator with an infinite liste on the right side
+=item use of rational numbers as a default
+
+=end pod
+
+sub infix:<choose> { [*] $^n - $^p ^.. $n Z/ 1 .. * }
+ 
+say 5 choose 3;