On Thu, Nov 17, 2011 at 5:38 PM, Jon Rafkind <[email protected]> wrote: > On 11/17/2011 01:24 PM, Jon Rafkind wrote: >> >> On 11/17/2011 01:20 PM, Ryan Culpepper wrote: >>> >>> On 11/17/2011 12:28 PM, Jon Rafkind wrote: >>>> >>>> I have some code that deconstructs and reconstructs a syntax object. I'm >>>> pretty sure this code is at fault for not adding the proper lexical >>>> context back on so I get an error about 'no #%app bound'. >>>> >>>> (syntax-parse form >>>> [(form ...) >>>> (with-syntax ([(form* ...) (map honu->racket (syntax->list #'(form >>>> ...)))]) >>>> (datum->syntax forms >>>> #'(form* ...) >>>> forms >>>> forms))] >>>> >>>> I had hoped that datum->syntax would add the original lexical context >>>> back on, is it not doing what I hoped? >>> >>> No, the datum->syntax there is a no-op, because #'(form* ...) is already >>> a syntax object, and datum->syntax stops when it hits something that's >>> already a syntax object. >>> >>> You should do something like this instead: >>> >>> (datum->syntax forms >>> (map honu->racket (syntax->list #'(form ...))) >>> forms >>> forms) >>> >> >> Ok thanks, that solved the problem. For future reference if I have a more >> complicated use case is there a way to put the original lexical context back >> on the new syntax object? >> >> If such a function could exist it should go into unstable/syntax since I >> keep forgetting how to reconstruct the lexical context. > > FWIW converting a syntax object to a list and then passing that to > datum->syntax works as well. > > (with-syntax ([(form* ...) (map honu->racket (syntax->list #'(form ...)))]) > (datum->syntax forms (syntax->list #'(form* ...)) forms forms))
(with-syntax ([(form* ...) e]) (syntax->list #'(form* ...))) is just a slower version of 'e' (unless e is a syntax object or if there is an error, neither of which apply here). Robby _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
