On Thu, Dec 09, 2010 at 12:36:09PM -0800, Gordon Tisher wrote: > On 09/12/2010 12:01 PM, Alan Post wrote: > > I'm working on my PEG parser, in particular the interface between > > the parse tree and the code one can attach to productions that > > are executed on a successful parse. > > > > I've arranged for the two predicate operations, & and !, to not add > > any output to the parse tree. That means that the following > > production: > > > > rule <- &a !b "c" > > This will never match anything, unless a == "c" >
It's an example showing the essential idea, I understand it looks likely to be wrong. > If you want to select only certain results from a sequence, use > variables to capture their results and an action to return the result of > any desired function of their values: > > Rule <- &a:x "c":y -> f(x,y) > Does your example imply: Rule <- &a "c" -> f() That is, if no rules are tagged, there are no arguments to f? Des it also imply: Rule <- &a:y "c":x -> f(x,y) Namely, that order of tagged rules doesn't matter, and that the signature for |f| accepts keyword arguments rather than positional arguments? Thank you, -Alan -- .i ko djuno fi le do sevzi _______________________________________________ PEG mailing list PEG@lists.csail.mit.edu https://lists.csail.mit.edu/mailman/listinfo/peg
