2015-08-04: add a closure example

add a closure example

diff --git a/examples/closure.w b/examples/closure.w
new file mode 100644
--- /dev/null
+++ b/examples/closure.w
@@ -0,0 +1,26 @@
+#!/usr/bin/env sh
+# -*- wisp -*-
+exec guile -L $(dirname $(dirname $(realpath "$0"))) --language=wisp -e '(@@ (examples closure) main)' -s "$0" "$@"
+; !#
+
+;; A simple example for a closure
+
+
+define counting-closure ; simple variable
+  let : : counter 0 ; provide counter to hold local data
+    lambda () ; the variable is bound to a function -> callable
+      set! counter : 1+ counter ; adjust the counter shared by all function calls
+      . counter
+
+
+; counter is created outside the function definition (lambda), so the
+; change survives over function calls. It is function-local data.
+
+
+define : main args
+         display : counting-closure
+         newline ; 1
+         display : counting-closure
+         newline ; 2
+         display : counting-closure
+         newline ; 3