I am having hard time making sense of GHC.Conc.   Is there a writeup that describes the significance of "#", or the meaning of "primOp" and "primType"?

Thanks

Daryoush

On Sun, Dec 7, 2008 at 11:48 PM, Don Stewart <dons@galois.com> wrote:
dmehrtash:
>    Any idea was the atomically# mean in the following code?
>
>    atomically :: STM a -> IO a
>    atomically (STM m) = IO (\s -> (atomically# m) s )
>
>    Code is from GHC.Conc module
>    [1]http://www.haskell.org/ghc/docs/6.6/html/libraries/base/GHC-Conc.html

It is a primitive hook into the runtime, where transactional memory is
implemented.

It is documented in the primops module in the GHC source,

   $ cd ghc/compiler/prelude/

   ------------------------------------------------------------------------
   section "STM-accessible Mutable Variables"
   ------------------------------------------------------------------------

   primtype TVar# s a

   primop  AtomicallyOp "atomically#" GenPrimOp
         (State# RealWorld -> (# State# RealWorld, a #) )
      -> State# RealWorld -> (# State# RealWorld, a #)
      with
      out_of_line = True
      has_side_effects = True

   primop  RetryOp "retry#" GenPrimOp
      State# RealWorld -> (# State# RealWorld, a #)
      with
      out_of_line = True
      has_side_effects = True


Along with other primitives like:

------------------------------------------------------------------------
section "Parallelism"
------------------------------------------------------------------------

   primop  ParOp "par#" GenPrimOp
      a -> Int#
      with
         -- Note that Par is lazy to avoid that the sparked thing
         -- gets evaluted strictly, which it should *not* be
      has_side_effects = True

-- Don