Thanks for reporting this. GHC should instead reject
the program: it doesn't make sense to derive instances
for types with existentially quantified constructors.
I'll commit a fix today, and update the documentation to explain it.
Simon
| -----Original Message-----
| From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
| Sent: 06 November 1999 16:19
| To: [EMAIL PROTECTED]
| Subject: Deriving instances of existentials
|
|
| The program
|
| data Ex = forall a. Ex [a] deriving Eq
| main = print (Ex "abc" == Ex "abc")
|
| causes ghc-4.04 to die with
|
| Subst.lhs:199: Non-exhaustive patterns in function zip_ty_env
|
| --
| __("< Marcin Kowalczyk * [EMAIL PROTECTED]
| http://qrczak.ids.net.pl/
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|
