[Agda] Implementation of abstract vs. irrelevance

Andrea Vezzosi sanzhiyan at gmail.com
Mon May 13 21:53:58 CEST 2013

I've grepped the code a bit and it seems that the speedup was mainly
because abstract definitions are skipped by the termination checker [1],
hence avoiding the instantiation of metavariables.

In my case a syntax for non-recursive definitions would solve the slowdown,
but it seems like a better solution could be to teach the termination
checker how to share work between different instantiations of the same
metavariable, if that's possible.

The code:
[1] https://code.google.com/p/agda/issues/detail?id=847

On Mon, May 13, 2013 at 1:45 PM, Andreas Abel <andreas.abel at ifi.lmu.de>wrote:

> Hi Andrea,
> "abstract" means that this definition is only expanded when checking other
> "abstract" definitions.
> Irrelevant arguments are not compared during equality checking, however,
> they might still be computed for other reasons, e.g. to determine their
> precise set of free variables.  Substitution also has to traverse
> irrelevant arguments, due to the lack of explicit substitutions in the Agda
> engine.
> The implementation of these features is scattered all over the Agda engine
> (TypeChecking.*), you might wanna grep for "AbstractMode" and "releva" to
> get to interesting source locations.
> Cheers,
> Andreas
> On 12.05.2013 12:00, Andrea Vezzosi wrote:
>> Hi,
>> I've noticed some very promising speedups by making definitions abstract
>> in addition to irrelevant and I'd like to understand why.
>> Skimming the code I couldn't figure out where the main pieces of the
>> implementation of these features are, is there a commentary on how they
>> are implemented? And what work does abstract save on top of irrelevance?
>> Thanks,
>>     Andrea
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