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

Ivan Lazar Miljenovic ivan.miljenovic at
Fri Mar 15 12:12:47 CET 2013

On 15 March 2013 22:05, Roman Cheplyaka <roma at> wrote:
> * 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.

And ghc-the-library, which means that anything that uses
ghc-as-a-library (and indeed even Cabal-as-a-library) no longer has a
choice of which version of parsec they use.

> Roman
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Ivan Lazar Miljenovic
Ivan.Miljenovic at

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