Ajout message erreur nobre invalide argument

src/migl/lisp/LispError.java

@@ -7,6 +7,8 @@ package migl.lisp;
  *
  */
 public class LispError extends Exception {
+	
+	public static final String ERR_NUM_ARG = "Invalid number of operands";
 
     /**
      * Fake serial version UID