existential-quantifier.md

@@ -8,4 +8,13 @@ type Any = exists a . Typeable a => a
 
 sameType :: Any -> Any -> Bool
 sameType x y = typeOf x == typeOf y
+
 ```
+
+
+When existentials appear in the contravarient position such as above, they can be desugared into rank-n types with foralls. if existentials are allowed in the covarient position, then support for FirstClassExistentials? is needed.
+
+## Support
+
+
+Jhc currently supports the existential syntax anywhere a type is accepted, but will report an error if one is used in a covariant position.