On 6/11/07, Ian Lynagh <[EMAIL PROTECTED]> wrote:
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
Bar
Baz
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
http://hackage.haskell.org/trac/hackage/wiki/CabalConfigurations
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 { ... }
The current syntax looks like this:
Name: Foo
Version: 0.1
...
Flag name {
Description: ...
}
...
Library {
Build-Depends: ...
if os(freebsd) && flag(foo) {
Build-Depends: ...
}
some-flag: ...
}
Executable name {
...
}
...
}
I first parse it into the general syntactic constructs
(field-description, section, or if-statement) and then transform it
into something like an AST which then gets parsed into the existing
back-end structure, depending on the flags and available dependencies.
The code however is rather ugly and ad-hoc. But since we won't need
the full parsec anyways, maybe i can extract some combinators and will
be fine.
/Thomas
--
"Remember! Everytime you say 'Web 2.0' God kills a startup!" -
userfriendly.org, Jul 31, 2006
_______________________________________________
cabal-devel mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/cabal-devel
