Adds method to detect undefined variables.

Author: apblack

undefined.grace

@@ -0,0 +1,24 @@
+var v
+
+method isUndefined(block) {
+    try {
+        block.apply.asString
+        return false
+    } catch { e:UninitializedVariable →
+        return true
+    }
+}
+
+if (isUndefined{v}) then {
+    print "v is undefined"
+} else {
+    print(v)
+}
+
+v := 5
+
+if (isUndefined{v}) then {
+    print "v is undefined"
+} else {
+    print(v)
+}