On 11 March 2005 07:44, Adrian Hey wrote:

On Thursday 10 Mar 2005 1:47 pm, Malcolm Wallace wrote:

...

I think it is something to do with the regular expression describing legal Cabal package names. A package name basically has three components: name, version number, and tag. The middle part, the version number, may contain dots, but I imagine the outer parts, the name and tag, may not?

Thanks. What's a "tag", BTW? (Cabal docs don't mention it AFAICS, but maybe I've missed something).

The tag is part of the version: a version has the form version ::= digit+ ('.' digit+)* ('-' alphanum+)* Tags are largely ignored by Cabal, they're just for adding useful information to a version (eg. you might add a tag for platform type, release date, or compiled-by). In particular, the tags are ignored in the ordering relation between versions. A package name currently has the form pkgname ::= alphanum+ ('-' alphanum+)* and a package identifier has the form pkgid ::= pkgname ['-' version] Allowing dashes in package names is quite common (look at the names of RPMs on a Linux system, or the packages on a FreeBSD system, for example). We already have problems with pkgids like "foo-1", which is ambiguous. The tools reject ambiguous package identifiers. Allowing '.' in a package name would introduce more possibilities for ambiguity: even 'foo-1.0' becomes ambiguous. So it's not simply a case of generalising the syntax slightly: we need to specify how to resolve the ambiguity. Restricting the components of the package name to start with an alphabetic character only seems a possibility. Cheers, Simon