2015-01-26: added example map-product-sums.w

added example map-product-sums.w

diff --git a/examples/map-product-sums.w b/examples/map-product-sums.w
new file mode 100644
--- /dev/null
+++ b/examples/map-product-sums.w
@@ -0,0 +1,23 @@
+#!/usr/bin/env sh
+exec guile -L $(dirname $(dirname $(realpath "$0"))) --language=wisp -e '(@@ (examples map-product-sums) main)' -s "$0" "$@"
+; !#
+
+use-modules : (srfi srfi-42) 
+
+define-module : examples map-product-sums
+
+define : list-product-sums list-of-numbers
+       . "return a list with the sum of the products of each number with all other numbers.
+
+         >>> map-product-sums '(2 4 6)
+         (list (+ (* 2 4) (* 2 6)) (+ (* 4 2) (* 4 6)) (+ (* 6 2) (* 6 4)))
+         "
+       map (lambda (x) (apply + x))
+           list-ec (: i list-of-numbers)
+               map (lambda (x) (* i x))
+                   list-ec (: j list-of-numbers) (if (= i j) 0 j)
+
+
+define : main . args
+  write : list-product-sums '(2 4 6)
+