On 6/11/07, Ian Lynagh
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