[Haskell-cafe] Re: Template Haskell: exchanging information between 'splicers'

jean-christophe mincke jeanchristophe.mincke at gmail.com
Mon Nov 29 10:04:33 CET 2010


I am using GHC 6.12.3

Here a reproduction:

in the file Template.hs

proc () = runIO $ do runQ [|1+1|]
proc' () = [|1+1|]

In the file Main.hs

i1 = $(proc ())      -- fails at compile time with "Segmentation
fault/access violation in generated code". Maybe is it the expected
behavior, I do not know.
i2 = $(proc' ())     -- sucessfull

i3 = proc() -- sucessful but proc is executed at "runtime"

main = ...

Hope it is clear enough otherwise let me know.



On Mon, Nov 29, 2010 at 4:45 AM, <oleg at okmij.org> wrote:

> Hello!
> > But, please, correct me if I am wrong, in your example, the splicer are
> > executed at run time and not at compile time.
> With TH, it becomes a bit difficult to tell what is exactly `compile
> time'. One can say however that when the code is ready to be spliced
> in at the top level, the IO actions in its splices must have been
> completed.
> > I have modified your example to make it run at compile time and I get a
> > (compile time) segmentation fault.
> As I mentioned, the code was specifically designed to cause something
> like segmentation fault. Sneaking out free variables is definitely the
> bad thing. The principle of exchanging data between splices (using
> runQ/runIO) is valid and could be used for good things, too.
> I am wondering though what GHC version and command-line parameters are
> you using? On my system. with GHC 6.10.3, I tried running the original
> and modified code in GHCi and GHC (with and without -O2) and did not
> get segmentation fault. Could you provide more details about your
> system so to reproduce the segfault? I think Simon Peyton-Jones would
> really like to know all that.
>        Cheers,
>        Oleg
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