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?
The StgSyn abstract syntax has an UpdateFlag on each StgRhs which lets you turn off the update, and I believe the code generator will respect it although it isn't actually ever turned off at the moment.
Indeed that works: I added a stg2stg transformation phase that removes the flag on some thunks (with hard-coded names for now :-)) and the generated code works as expected. I’m now thinking how I can allow the programmer to annotate thunks as non-updateable, and how to carry that information to the stg phase. Greetings, Joachim -- Dipl.-Math. Dipl.-Inform. Joachim Breitner Wissenschaftlicher Mitarbeiter http://pp.info.uni-karlsruhe.de/~breitner