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

On 15 March 2013 22:05, Roman Cheplyaka wrote:

* Heinrich Apfelmus [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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