Re: Strange behavior when using stable names inside ghci?

28 Jun 2012

      Hi Facundo,
...
The program below when loaded in ghci prints always False, and when
compiled with ghc it prints True
...
From above, I guess the code is not compiled in ghci, which means
byte-code is used insted of object-code.
If what matter here is "to get same result in ghci and compiled code",
invoking ghci with object code compilation option[1] may help. E.g.
start ghci with:

  $ ghci  -fobject-code

Below is a sample session with your code. I saved it as "UCSN.hs".

  $ ls
  UCSN.hs
  $ ghc-7.4.1 --interactive UCSN.hs
  GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
  Loading package ghc-prim ... linking ... done.
  Loading package integer-gmp ... linking ... done.
  Loading package base ... linking ... done.
  [1 of 1] Compiling UCSN             ( UCSN.hs, interpreted )
  Ok, modules loaded: UCSN.
  ghci> :main
  type enter
  False
  ghci> :q
  Leaving GHCi.

Invoking again, with "-fobject-code". Note the absense of "interpreted" message:

  $ ghc-7.4.1 --interactive -fobject-code UCSN.hs
  GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
  Loading package ghc-prim ... linking ... done.
  Loading package integer-gmp ... linking ... done.
  Loading package base ... linking ... done.
  [1 of 1] Compiling UCSN             ( UCSN.hs, UCSN.o )
  Ok, modules loaded: UCSN.
  ghci> :main
  type enter
  True
  ghci> :q
  Leaving GHCi.

Now we have "UCSN.hi" and "UCSN.o".

  $ ls
  UCSN.hi  UCSN.hs  UCSN.o

Invoking ghci again, without "-fobject-code".
No "interpreted" message. Showing 'True' with main.

  $ ghc-7.4.1 --interactive UCSN.hs
  GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
  Loading package ghc-prim ... linking ... done.
  Loading package integer-gmp ... linking ... done.
  Loading package base ... linking ... done.
  Ok, modules loaded: UCSN.
  ghci> :main
  type enter
  True
  ghci> :q
  Leaving GHCi.

Hope these help.

[1]: http://www.haskell.org/ghc/docs/latest/html/users_guide/options-phases.html#...

Regards,
--
Atsuro

On Thu, Jun 28, 2012 at 6:41 AM, Facundo Domínguez
 wrote:
...
Hi,
 The program below when loaded in ghci prints always False, and when
compiled with ghc it prints True. I'm using ghc-7.4.1 and I cannot
quite explain such behavior. Any hints?
Thanks in advance,
Facundo
{-# LANGUAGE GADTs #-}
import System.Mem.StableName
import Unsafe.Coerce
import GHC.Conc
data D where
  D :: a -> b -> D
main = do
 putStr "type enter"
 s <- getLine
 let i = fromEnum$ head$ s++"0"
     d = D i i
 case d of
   D a b -> do
       let a' = a
       sn0 <- pseq a'$ makeStableName a'
       sn1 <- pseq b$ makeStableName b
       print (sn0==unsafeCoerce sn1)
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Re: Strange behavior when using stable names inside ghci?

Atsuro Hoshino