Experimentally run ST in a fake world
Needs RevisionPublic

Authored by dfeuer on Mar 23 2017, 2:34 AM.



Currently, ST actions are instantiated at s = RealWorld when
run. We'd really like to treat ST and IO somewhat differently
for demand analysis, which means we need to have a way to distinguish
them. The most conservative option seems to be to use a different
State# token type.

This commit experimentally (and with a big hammer) adds a new
FakeWorld primitive type, a fakeWorld# :: State# FakeWorld
primitive token, and a runFW# (run in a fake world) token.
It then uses runFW# to implement runST. Let's see what happens.

Diff Detail

rGHC Glasgow Haskell Compiler
Lint WarningsExcuse: Linty
Warningcompiler/basicTypes/MkId.hs:1119TXT3Line Too Long
Warningcompiler/basicTypes/MkId.hs:1129TXT3Line Too Long
Warningcompiler/basicTypes/MkId.hs:1574TXT3Line Too Long
Warningcompiler/coreSyn/CorePrep.hs:822TXT3Line Too Long
Warningcompiler/coreSyn/CoreUnfold.hs:523TXT3Line Too Long
Warningcompiler/prelude/TysPrim.hs:177TXT3Line Too Long
Warningcompiler/prelude/TysPrim.hs:195TXT3Line Too Long
No Unit Test Coverage
Build Status
Buildable 15288
Build 25529: [GHC] Linux/amd64: Patch building
Build 25528: [GHC] OSX/amd64: Continuous Integration
Build 25527: [GHC] Windows/amd64: Continuous Integration
Build 25526: arc lint + arc unit
dfeuer created this revision.Mar 23 2017, 2:34 AM
dfeuer updated this revision to Diff 11850.Mar 23 2017, 3:11 AM
  • Change runST definition
dfeuer updated this revision to Diff 11851.Mar 23 2017, 8:37 AM
  • Change runST definition
bgamari requested changes to this revision.Mar 29 2017, 4:24 PM

What needs to happen to finish this up, @dfeuer?


It really seems like this should share code with runRWId.


It seems like ST should be mentioned here.

This revision now requires changes to proceed.Mar 29 2017, 4:24 PM

Is this still pertinent?


Is this an exact copy of the above code (except for fakeWorldPrimId)? How about a local refactoring?

Is this still pertinent?

Perhaps, but it requires a tad more work since Core Prep currently doesn't do any substitution in types (which we must do to instantiate State#'s argument) . I think we want to preserve this property, so we would likely need to do something like adding a substitution in the runFW# case in cpeApp.


I agree. @dfeuer, in my local branch where I debugged this I refactored this to,

-- Given an expression @runRW# arg arg1 .. argN@, construct
-- @arg realWorld# arg1 .. argN@, beta reducing if possible.
apply_realWorld :: CorePrepEnv -> CoreExpr -> [ArgInfo] -> Int -> UniqSM (Floats, CpeRhs)
apply_realWorld env arg args depth =
  pprTrace "apply_reawlWorld" (ppr arg $$ ppr args $$ ppr env) $
  case arg of
    Lam s body  ->
      let env'  = extendCorePrepEnv env s realWorldPrimId
      in cpe_app env' body args (depth - 1)
    _           ->
      let args' = CpeApp (Var realWorldPrimId) : args
      in cpe_app env  arg  args' depth

With the appropriate rewrites of the cases in cpe_app.

dfeuer updated this revision to Diff 12138.Apr 15 2017, 3:22 PM
  • Change runST definition
  • Tighten up; comment up

What about a testcase?


It looks like your base commit is incorrect.


This line should really be split up at some point. I'll take care of this after merging this.


Base commit again.

bgamari requested changes to this revision.Apr 17 2017, 10:23 AM
This revision now requires changes to proceed.Apr 17 2017, 10:23 AM

I realize this is kind of inconvenient to change, but I would be happier if we just called this thing stWorld#, runST#, etc. rather than having to remember the trivia that fakeWorld# is used for ST.

austin resigned from this revision.Nov 9 2017, 11:36 AM