deeqSeq proposal

Lennart Augustsson lennart at
Tue Apr 11 17:37:50 EDT 2006

Yes, I realize than dynamic idempotence is not the same as
cycle detection.  I still worry. :)

I think expectance is in the eye of the beholder.  The reason
that (the pure subset of) pH was a proper implementation of
Haskell was because we were not over-specifying the semantics
originally.  I would hate to do that now.

	-- Lennart

Simon Peyton-Jones wrote:
> | Well, my worry was partly about the suggested version of deepSeq that
> | would not diverge on circular structures (since circular structures
> | are just one way to implement "infinite" data structures).
> Dynamic idempotence is not the same as detecting circular structures.
> Deepseqing a circular structure should definitely diverge, as it would
> as if it was infinite.  Idempotence changes the operational behaviour,
> but not the denotational behaviour.  So that part of the worry is ok.
> But since the dynamic-idempotence operational behaviour is (as I
> understand the proposal) the whole point, it's true that the
> implementation would be constrained.  In the same kind of way that we
> expect call-by-need rather than call-by-name.  
> S

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