Non-updateable thunks

[Simon Marlow]

On 03/08/2012 10:29, Joachim Breitner wrote:
> Hi Simon,
>
> Am Freitag, den 03.08.2012, 09:28 +0100 schrieb Simon Marlow:
>>> My question is: Has anybody worked in that direction? And are there any
>>> fundamental problems with the current RTS implementation and such
>>> closures?
>>
>> Long ago GHC used to have an "update analyser" which would detect some
>> thunks that would never be re-entered and omit the update frame on them.
>>    I wrote a paper about this many years ago, and there were other people
>> working on similar ideas, some using types (e.g. linear types) - google
>> for "update avoidance".  As I understand it you want to omit doing some
>> updates in order to avoid space leaks, which is slightly different.
>
> Thanks for the pointers, I will have a look. Why was the update analyser
> removed from GHC?

It was expensive and had very little benefit - most thunks that were 
deemed non-updatable by the analysis were also strict, so update 
analysis did very little in the presence of strictness analysis.

Cheers,
	Simon