<html> <head> <meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type"> </head> <body bgcolor="#FFFFFF" text="#000000"> <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"> <pre style="color: rgb(0, 0, 0); font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; word-wrap: break-word; white-space: pre-wrap; ">The following example has some tricky hygiene issues that I don't quite understand. The point of the code is to have a form that creates macros by analyzing the pattern and template. The issue is why do I have to use a name other than 'name' for the pattern variable on the line where it says 'HERE'. If I use the 'name' pattern variable then the syntax-parse form generated by 'make-transformer' will use the wrong lexical context for the literal set. I don't see how the lexical context of the outer 'name' differs from the inner 'new-name', other than the 'new-name' has an extra mark on it. Is that the issue? I tried all sorts of debugging techniques but I can't tell if 'name' has a different lexical context than 'new-name'. I see that marks affect 'bound-identifier=?' but they don't seem to effect 'free-identifier=?' which is what syntax/parse uses to compare literals. #lang racket (require (for-syntax syntax/parse) (for-meta 2 racket/base syntax/parse)) ;; defines a literal and a literal-set that contains the literal (module literals racket/base (require syntax/parse) (provide literal1 literals) (define literal1 0) (define-literal-set literals (literal1))) (module transformer racket/base (require (for-syntax syntax/parse (submod "." ".." literals) racket/base) racket/splicing (for-meta 2 syntax/parse racket/base)) (begin-for-syntax (define-syntax (make-transformer stx) (syntax-parse stx [(_ name pattern template) #'#'(lambda (stx) (syntax-parse stx #:literal-sets ([literals #:at name]) [pattern template]))]))) (provide define-new-syntax) (define-syntax (define-new-syntax stx) (syntax-parse stx [(_ name pattern template) #'(splicing-let-syntax ([make (lambda (stx) (syntax-parse stx [(_ new-name) ;; HERE! If you change this to 'name' it will break (with-syntax ([output (make-transformer name pattern template)]) #'(define-syntax new-name output))]))]) ; change to 'name' too (make name))]))) (require (submod "." literals) (for-syntax (submod "." literals)) (for-meta 2 (submod "." literals)) (submod "." transformer)) (begin-for-syntax (define-syntax (test stx) (syntax-parse stx #:literal-sets (literals) [(_ literal1) #''ok]))) ;; if `literal1' isn't matched as a literal then the call to ;; (test literal1) will fail (define-new-syntax x [_ literal1] (begin (test literal1) #'0)) (x literal1) More explanation about this code: It was recommended to me that the code which analyzes the pattern and template should execute at a phase higher than the phase of the pattern/template. Since the macro is defined at phase 0 the pattern and template live in phase 1 and should be analyzed in phase 2. I cannot just invoke a macro inside the body of 'define-new-syntax' on the 'pattern' and 'template' parameters because then the macro would get the literal syntax objects #'pattern and #'template instead of the syntax they are bound to. As in (define-syntax (define-new-syntax stx) (syntax-parse stx [(_ name pattern template) (analyze pattern template)])) Nor would it be right to make 'analyze' a function at phase 1 and invoke it as (analyze #'pattern #'template) because I need to execute analyze at phase 2. I get to phase 2 by using a let-syntax trampoline in the output of the 'define-new-syntax' macro. The 'pattern' and 'template' variables will have been replaced with their matched syntax as appropriate so the 'make-transformer' macro will operate on the arguments used at the 'define-new-syntax' use-site. The resulting 'x' macro does nothing except invoke a phase 1 macro. This test is necessary to insure that 'literal1' was matched as a literal and not a pattern variable.</pre> On 05/17/2012 02:52 PM, Jon Rafkind wrote: <blockquote cite="mid:4FB564F7.6030106@cs.utah.edu" type="cite"> <meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type"> Ok I see from the syntax/parse source that it uses lctx as the first argument to datum->syntax, so that mostly answers my question. On 05/17/2012 02:41 PM, Jon Rafkind wrote: <blockquote cite="mid:4FB56262.901@cs.utah.edu" type="cite"> <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"> What exactly are the semantics of #:at inside a #:literal-sets ([x #:at y]) ? From the docs " <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"> <span style="color: rgb(0, 0, 0); font-family: serif; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); font-size: medium; display: inline !important; float: none; ">If the <span class="RktPn" style="font-family: monospace; white-space: normal; color: rgb(132, 60, 36); font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); ">#:at<span style="color: rgb(0, 0, 0); font-family: serif; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); font-size: medium; display: inline !important; float: none; "> keyword is given, the lexical context of the <span class="RktVar" style="font-family: monospace; white-space: normal; color: rgb(38, 38, 128); font-style: italic; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); ">lctx<span style="color: rgb(0, 0, 0); font-family: serif; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); font-size: medium; display: inline !important; float: none; "> term is used to determine which identifiers in the patterns are treated as literals;". In what way is 'lctx' used? <fieldset class="mimeAttachmentHeader"></fieldset> <pre wrap="">____________________ Racket Users list: <a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://lists.racket-lang.org/users">http://lists.racket-lang.org/users</a> </pre> </blockquote> <fieldset class="mimeAttachmentHeader"></fieldset> <pre wrap="">____________________ Racket Users list: <a class="moz-txt-link-freetext" href="http://lists.racket-lang.org/users">http://lists.racket-lang.org/users</a> </pre> </blockquote> </body> </html>