CDE

Task/Constrained-genericity/E/constrained-genericity.e

@@ -0,0 +1,14 @@
+/** Guard accepting only objects with an 'eat' method */
+def Eatable {
+    to coerce(specimen, ejector) {
+        if (Ref.isNear(specimen) && specimen.__respondsTo("eat", 0)) {
+            return specimen
+        } else {
+            throw.eject(ejector, `inedible: $specimen`)
+        }
+    }
+}
+
+def makeFoodBox() {
+    return [].diverge(Eatable) # A guard-constrained list
+}