Collapsing HsForAllTy, again

Simon Peyton Jones simonpj at
Thu Apr 9 22:14:02 UTC 2015

Hmm.  I’m not sure what the motivation is either.  Try dropping it out and see if anything goes wrong.


From: ghc-devs [mailto:ghc-devs-bounces at] On Behalf Of Alan & Kim Zimmerman
Sent: 09 April 2015 22:15
To: ghc-devs at
Subject: Collapsing HsForAllTy, again

With the help of Jan Stolarek I tracked down the HsForAllTy flattening to
This function takes any nested HsForAllTy's where the top one does not have a context defined, and collapses them into a single one.
I do not know what the motivation for this is, and if it perhaps speeds up or simplifies further compilation.
But now that API Annotations have arrived, making sure we do not lose the annotations for the sub-HsForAllTy  causes significant gymnastics in the parser [1].
So my question is, is there a good reason to continue doing this, given the trade-off in parser complexity.

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