Gotcha! Thanks! And also thanks Alex, you gave me the right answer, I just didn't understand.
On Monday, July 24, 2017 at 2:28:32 PM UTC-4, Philip McGrath wrote: > The error message from `id:my-id` seems very confusing. You can't use the > colon notation with syntax classes that take arguments. You have to write > something like: > > > > (define-syntax (my-let stx) > (syntax-parse stx > [(_ ([id binding] ...) body ... last-body) > #:declare id (my-id 'let "an identifier to bind") > #'(let ([id binding] ...) body ... last-body)])) > > > You might want to look at `expr/c` for an example of a syntax class that > takes arguments: > http://docs.racket-lang.org/syntax/Library_Syntax_Classes_and_Literal_Sets.html?q=~expr%2Fc#%28def._%28%28lib._syntax%2Fparse..rkt%29._expr%2Fc%29%29 > > > > -Philip > > > > On Mon, Jul 24, 2017 at 1:18 PM, Sam Waxman <samw...@gmail.com> wrote: > Sorry, I think I need to elaborate a bit more! > > > > I've written code as follows > > > > (define-syntax-class my-id > > (pattern id > > #:do (if (identifier? #'id) (values) > > (raise-user-error (~a "Expected id: " (syntax->datum #'id)))))) > > > > (define-syntax (my-let stx) > > (syntax-parse stx > > [(_ ([id:my-id binding] ...) body ... last-body) > > #'(let ([id binding] ...) body ... last-body)])) > > > > (define-syntax (reassign stx) > > (syntax-parse stx > > [(_ id:my-id new-value) > > #'(set! id new-value)])) > > > > ... other syntax rules using my-id as a syntax class > > > > I enjoy using syntax classes to check that my arguments are id's, but what I > don't enjoy is how limited my error message is. (I don't want to use Rackets. > The end users for this are students using very simple self-defined languages, > and the error messages should be very intuitive, so my-id > > is just id but with my own error.) > > > > What I'd like to do is format my errors more like > > "let: Expected an identifier to bind but got 3" > > "reassign: Expected an identifier to reassign but got 3." > > > > The way I planned to do this was to pass arguments into my syntax class. In > the racket documentation, it states this is possible. The forms of > define-syntax-class are as follows. > > > > (define-syntax-class name-id stxclass-option ... > > stxclass-variant ...+) > > (define-syntax-class (name-id . kw-formals) stxclass-option ... > > stxclass-variant ...+) > > > > I'm hoping to use the second form to write something like the following > > > > (define-syntax-class (my-id name description) > > (pattern id > > #:do (if (identifier? #'id) (values) > > (raise-syntax-error name > > (~a " expected " description but got (syntax->datum > #'id)))))) > > > > This way I could write my let as > > > > (define-syntax (my-let stx) > > (syntax-parse stx > > [(_ ([id:(my-id 'let "an identifier to bind") binding] ...) body ... > last-body) > > #'(let ([id binding] ...) body ... last-body)])) > > > > (or to make this look cleaner, I could have a line of code before this that > says (define let-id (my-id 'let "an identifier to bind")) I don't think that > would exactly work, but I'm sure it's doable in some way) > > > > The only thing I'm having problems with is that apparently that isn't the > right way to use the formals. When I try writing it the original way but with > the updated my-id version, I get > > > > id:my-id: expected 1 positional argument; got 0 positional arguments in: > id:my-id > > > > and when I write it with the parentheses like I did in the last example I get > > > > my-let: expected more terms at: () within: (my-let ([x 2]) 1) in: (my-let ([x > 2]) 1) > > > > On Monday, July 24, 2017 at 1:19:06 PM UTC-4, Alex Knauth wrote: > > > > > On Jul 24, 2017, at 1:06 PM, Sam Waxman <samw...@gmail.com> wrote: > > > > > > > > > Probably a silly question but I can't figure out how to get this working. > > > > > > I want to have a syntax class that I can pass arguments into. So, > > > > > > (define-syntax-class (my-syn-class argument) > > > ... > > > ) > > > > > > (syntax-parse #'some-syntax > > > [(_ x:*????*)]) > > > > > > > > > In place of *????* what do I write to pass the argument into my syntax > > class? > > > I tried > > > > > > (syntax-parse #'some-syntax > > > [(_ x:(my-id *my-argument*)]) > > > > > > but this doesn't appear to work. > > > > > > Thanks in advance! > > > > > > > > > You have to use either ~var [1] or #:declare [2]. > > > > > > > > > [1]: > > http://docs.racket-lang.org/syntax/stxparse-patterns.html#%28elem._%28pattern-link._%28~7evar._s%2B%29%29%29 > > > [2]: > > http://docs.racket-lang.org/syntax/stxparse-specifying.html#%28part._.Pattern_.Directives%29 > > > > -- > > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users...@googlegroups.com. > > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. 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