New restrictions to open type families

Simon Peyton-Jones simonpj at
Fri Aug 23 12:46:22 CEST 2013


Thanks that's amazing!  I wonder if it'd be worth adding it, with commentary, (and attaching the files) as a Trac ticket?  I know its already fixed, but it's great to be able to say "to see an example of why this is vital, see Trac #8324", whereas email archives are more ephemeral somehow.


From: Glasgow-haskell-users [mailto:glasgow-haskell-users-bounces at] On Behalf Of Akio Takano
Sent: 23 August 2013 11:35
To: glasgow-haskell-users at; Richard Eisenberg
Subject: Fwd: New restrictions to open type families

(I forgot to send to the list, trying again)
Thank you very much for your detailed explanation!

On Fri, Aug 23, 2013 at 1:24 PM, Richard Eisenberg <eir at<mailto:eir at>> wrote:
This is a good question. Happily, there are at least two decent answers.

1) We're not sure that this problem cannot cause a segfault... it's just that we've been unable to produce one when trying. Perhaps we haven't tried hard enough.

I successfully constructed such an example.

- Akio

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