Compiler versions

7 Apr 2004

      Library folk

Below is a suggestion from George that initially appears to be about
Template Haskell: access to the GHC version identity.  But of course
it's not strictly a TH thing: we could simply provide a module

	module GHC.Version where
	   ghcVersion :: Int

and then you could import that module anywhere, including in your TH
program:

	import GHC.Version
	$( if ghcVersion > ... then ... )

And indeed such a thing might be more generally useful, across all
Haskell implementations not just GHC.  Perhaps it should be

     module System.Compiler where
	compilerName :: String
	releaseDate :: CalendarTime 	-- or (Day,Month,Year)?
	version :: (Int,Int)
	patchLevel :: Int

So then a program could ask whether it was being run by Hugs or GHC or
whatever.

Questions:

* Would this be a good thing to agree across compilers?

* What should the interface be?  I gave one possibility above; George
gives another.

* I imagine this'd be useful for the library infrastructure project,
somehow.

Would anyone like to run with this to get an interface agreed?  From the
GHC end we'd be happy to implement any agreed interface.

Simon

-----Original Message-----
From: George Russell [mailto:ger@informatik.uni-bremen.de] 
Sent: 07 April 2004 10:46
To: Simon Peyton-Jones
Subject: Re: mkName and qualified names

George Russell wrote:
...
incidentally you asked for priorities.  Mine are (still)
Oh, and another one,
(3) access to the current GHC version.  For example

    data GhcVersion

    instance Read GhcVersion
    instance Ord GhcVersion

    thisVersion :: GhcVersion

then you can do
    $( if thisVersion >= read "6.4.1"
       then
          [dd| -- use whizzo new features
             ...
             |]
       else
          [dd| -- sigh.  painful workaround for Luddites
             ...
             |]
       )

This isn't nearly as important to me as the other two suggestions
I made, however I presume it would be easier to implement.

best wishes and thanks,

George