[fix] remove space leaks in (,) by using strict state

[MangoIV]

• benchmarks on maintainer-list.nix give a baseline of 88M max residency, nice triangle of death and a bit over 4 seconds duration
• heap profile shows a lot of memory allocated to (,)
• removing usagge of (,) in own code didn't affect the profile
• changing to strict state improves memory from 88 to 40 max residency and runtime goes down by 1 second

[github-actions]

Nixpkgs diff

[infinisil]

Very nice, thanks a lot!

[infinisil]

Can I ask how you're doing the benchmarking? I don't have a lot of experience doing that with Haskell

[MangoIV]

Can I ask how you're doing the benchmarking? I don't have a lot of experience doing that with Haskell

Heap Profiling: compile the program with profiling (e.g. by using the --enable-profiling with cabal), then run the program with heap profiling enabled in the RTS, e.g. to break down by cost centre and output to an eventlog, +RTS -hc -l-au, then use haskellPackages.eventlog2html to visualize the heap profile.

Time profiling: almost the same, except you run with +RTS -p -l-au , then you can convert the eventlog to a json with haskellPackaes.hs-speedscope and load it into e.g. https://speedscope.app.

The GHC manual also has a section about profiling haskell programs:
https://downloads.haskell.org/ghc/latest/docs/users_guide/profiling.html

If you happen to have space leaks, you often can bring down max residency and run time at once, if you are lucky enough to find the space leak

[MangoIV]

lazy state is a huge red flag though, so that wasn't too hard, thankfully.

[infinisil]

Very useful, thanks!

[MangoIV]

I have gotten nixfmt fast enough to feasibly run on hacke-packges.nix and even though the pretty printer is much faster than the parser, it still got a pretty bad space leak

[MangoIV]

The big brown triangle is labeled with Int, which means that it's probably some arithmetic that is not forced.

[MangoIV]

and this is how it looks when it's gone.

[MangoIV]

(yeah, the space leak of the parser is still pretty bad, I just now fixed set to force its arguments...)

[MangoIV]

DocE uses lists, which is a really bad datatype for these sorts of things, so there's another space leak (orange triangle in the bottom right)