X-Git-Url: https://code.consxy.com/gitweb/gitweb.cgi?a=blobdiff_plain;f=src%2Fmain%2Fnvm%2Fbase.lisp;h=fc2db581e6395ae764753febb0c8d8f52e308626;hb=393d2cd66721b93bed149613ceb7ee4fdac408c2;hp=9d07e9b1280ff677b51faf1e65993f924c59cc80;hpb=aa474227efad1f00e26f762b597a1f18a9cc3be5;p=clnl

diff --git a/src/main/nvm/base.lisp b/src/main/nvm/base.lisp
index 9d07e9b..fc2db58 100644
--- a/src/main/nvm/base.lisp
+++ b/src/main/nvm/base.lisp
@@ -11,6 +11,23 @@
 (defvar *ticks* nil)
 (defvar *breeds* nil)
 
+(define-condition stop nil nil)
+
+(defmacro with-stop-handler (&rest forms)
+ "MACRO WITH-STOP-HANDLER &rest FORMS => HANDLED-FORM
+
+ARGUMENTS AND VALUES:
+
+  FORMS: body to be handled
+  HANDLED-FORM: body with handling
+
+DESCRIPTION:
+
+  WITH-STOP-HANDLER is a convenience macro to handle when
+  programs issue a stop condition.  When one does, a simple
+  :stop is returned."
+ `(handler-case (progn ,@forms) (stop (s) :stop)))
+
 (defstruct turtle who color heading xcor ycor (label "") (label-color 9.9d0) (size 1d0) shape)
 (defstruct patch color xcor ycor)