GADT problems

Philippa Cowderoy flippa at
Mon Sep 15 09:11:05 EDT 2008

[sent to list as well this time]

On Mon, 2008-09-15 at 14:00 +0100, Simon Peyton-Jones wrote:
> Ah -- you used an *existential* there!  Yes, existentially-bound type variables are rigid.  They stand for themselves, as it were.
> That resolves the mystery -- but it existentials admittedly introduce a new complication
> How should this be clarified?

For me, "existentially-bound variables are rigid" works well enough.
They're a somewhat non-obvious case of 'coming from an annotation'
though, and it does warrant mention.

Philippa Cowderoy <flippa at>

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