Am 24.08.2015 um 00:18 schrieb Jacques Garrigue:
> This is indeed a pretty difficult problem, as you must be careful of not
> changing the semantics of unification.
> Until recently, the only solution was to expand the type, as there was
> no static information cacheing whether an argument was used in the
> body or not.
> However, since relatively recent changes about variance information
> (the switch to 7 flags…), we actually have at least an approximation
> of which unifications must be done imperatively, and which needn’t
> be done at all.
> So it might be doable at least for part of the parameters.

That sounds interesting. What are the relevant variance flags?

> I would have to see the code to tell you more.
> As stated above, the real problem is the length of the cycles in the expanded
> graph.

I really do not think that this is related to any cycles. It is just
about large unfolded types. I attached a script to generate a meaningful
example. When I try to run ocamlbuild m_9.cmo, it takes ~30s already. A
preliminary patched version of the ocaml compiler can handle this
particular example in pretty much no time at all.

regards,

Christoph

-- 
Christoph Höger

Technische Universität Berlin
Fakultät IV - Elektrotechnik und Informatik
Übersetzerbau und Programmiersprachen

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E-Mail: christoph.hoeger@tu-berlin.de