Parsec as a Dependency?

Ian Lynagh igloo at
Mon Jun 11 07:49:42 EDT 2007

Hi Thomas,

On Sun, Jun 10, 2007 at 03:44:14PM +0200, Thomas Schilling wrote:
> now that .cabal files are getting a more complex syntax (due to
> configurations), I'd really like to use Parsec instead of lots of
> hand-written and hard to maintain parsing code.  By getting rid of
> ReadP-based field parsing, we'd also get proper error messages for
> field values.
> At the Parsec homepage I says that it's now included by default in
> GHC, Hugs and NHC,

As Simon said, unfortunately as of 6.8 it won't be included with GHC (as
things stand, at least).

alex+happy is another alternative, although I don't know off-hand if
hugs/nhc/... can build them currently.

Have you got a description of the grammar you want to parse?

I'd like it if we could say
    if flag(foo) {
        other-modules: Foo
        ghc-options: -wibble
which needs some sort of layout rule for the module list. If we go for
something like that then I wouldn't be surprised if this wasn't easiest
to parse with just ad-hoc code, which would avoid any dependencies and
give good error messages.

The parser would only parse it down to something like

    Cond (Flag "foo) [Pair "other-modules:" "Foo\n   Bar\n   Baz\n",
                      Pair "ghc-options:" "-wibble\n"]

and these would then be further parsed by their own little parsers.

Just looked at

I'd also suggest putting the top block of your example on that page in
    General { ... }
(or some better name) and the next two in
    Flag: fps_in_base { ... }
    Flag: debug { ... }


More information about the cabal-devel mailing list