Advance notice that I'd like to make Cabal depend on parsec

Roman Cheplyaka roma at
Fri Mar 15 12:05:06 CET 2013

* Heinrich Apfelmus <apfelmus at> [2013-03-15 10:38:37+0100]
> Duncan Coutts wrote:
> >Hi folks,
> >
> >I want to give you advance notice that I would like to make Cabal depend
> >on parsec. The implication is that GHC would therefore depend on parsec
> >and thus it would become a core package, rather than just a HP package.
> >So this would affect both GHC and the HP, though I hope not too much.
> >
> >[..]
> >
> >Why did I choose parsec? Practicality dictates that I can only use
> >things in the core libraries, and the nearest thing we have to that is
> >the parser lib that is in the HP. I tried to use happy but I could not
> >construct a grammar/lexer combo to handle the layout (also, happy is not
> >exactly known for its great error messages).
> Reuse is good, but the implication I'm worried about is this: Can I
> upgrade the  parsec  package installed on my system by doing a user
> install from  hackage ? Without an implementation of more flexible
> package installations (multiple versions installed simultaneously),
> any dependency of GHC has its version number essentially set into
> stone.

We've had that working for a long time. Right now I even have multiple
installed versions of Cabal-the-library itself.

It's not that Parsec would be automatically linked into each executable.
It's just that ghc-the-program would have Parsec linked into it.


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