|Posted by Nick Sabalausky|
in reply to Stephan
Posted in reply to Stephan
"Stephan" <email@example.com> wrote in message news:firstname.lastname@example.org...
> On 18.05.2011 05:47, Nick Sabalausky wrote:
>> Goldie Parsing System v0.5 is now out. This version focuses mainly on
> Great work.
> Is it possible to generate a parser for D with this ?
It should be possible to write a grammar that handles most of D. But there would be some awkwardness and corner cases that, to really be handled right, would need some enhancements I haven't put in yet.
- Nested comments aren't yet officially supported. GOLD (which Goldie is based on) will support them in the currently-in-beta v4.2 ( http://www.devincook.com/goldparser/v4.2.htm ). I intend to make Goldie fully compatible with all the new GOLD v4.2 features, but just haven't gotten to them yet. In the meantime, what you can do is lex the D source first, then go through the resulting token array removing everything from a "/+" token to its matching "+/" token (there will be a bunch of junk in between, including some error tokens, you can just rip it all out), and then send that through the parser.
- Another comment-related thing that'll be fixed with the v4.2 enhancements: Currently, GOLD and Goldie handle (non-nested) block comments by actually lexing what's inside the comment (and ignoring any errors). Normally this works out fine, but it does lead to some occasional edge-cases where the "*/" isn't handled right.
- D relies on certain disambiguation rules. For instance: "a*b" could be either a multiplication expression or a pointer declaration. D handles this by saying "if something can be either an expression or a declaration, then always interpret it as (umm...actually I forget which one it always chooses, but it's always that same one)". Goldie (and GOLD) currently doesn't have any conflict resolution. If you try to create a grammar that has such an ambiguity, you'll just get a "reduce-reduce conflict" error, or "shift-reduce" problems. The way to work around this is to design the grammar to completely conflate the two notions, so instead of having <Expression> and <Declaration>, you'd just have something like <ExprOrDecl>. Unfortunately, this isn't always easy, it does tend to obfuscate the grammar, it makes the nonterminals less meaningful, and it'll create much more work for your semantics pass. I do intend to solve this, but it'll probably be a very non-trival matter. More discussion (possibly a bit technical) on this issue is here: http://groups.google.com/group/gold-parsing-system/browse_thread/thread/5959e0cfef76ce68
FWIW, Goldie does include a lex-only grammar for D2, which could be used as a starting point (although it's possible I might have gotten some edge cases wrong regarding the decimal literals. Also, this grammar is currently ASCII-only, but that can easily be changed):