[racket] Introduction to syntax-parse

If you look in the Typed Racket implementation, you'll see lots phase-1
only uses of syntax-parse.

Sam
On Sep 24, 2013 3:21 PM, "Nick Sivo" <nicksivo at gmail.com> wrote:

> Why doesn't syntax/parse just provide everything at phases 0 and 1
> like the module 'sp below:
>
> (module sp racket/base
>   (require syntax/parse
>            (for-syntax syntax/parse))
>   (provide (all-from-out syntax/parse)
>            (for-syntax (all-from-out syntax/parse))))
>
> (require 'sp)
>
> (define-syntax (mylet stx)
>   (syntax-parse stx
>                 [(_ ([var-id rhs-expr] ...) body ...+)
>                  #'((lambda (var-id ...) body ...) rhs-expr ...)]))
>
> I've not done as much Racket programming as many of you, but I've yet
> to want syntax/parse in only phase 0.
>
> -Nick
>
> On Tue, Sep 24, 2013 at 10:21 AM, Laurent <laurent.orseau at gmail.com>
> wrote:
> > This is a quite common pitfall into which I have myself fallen a few
> times,
> > and I guess it's not the last time.
> >
> > How much work would be required to prevent people from falling into it
> ever
> > again?
> > Maybe saying so in the docs at the right place wouldn't hurt, but people
> may
> > still miss it.
> > Maybe making the error message more specific like "Did you forget to
> > (require (for-syntax syntax/parse)) ?" ? Or is it too specific?
> > Or pushing the idea further (and requiring more work, obviously),
> Racket's
> > errors could propose a list of packages where the unknown identifier can
> be
> > found, along with the require phase? Is xref able to do that currently?
> >
> > Laurent
> >
> >
> >
> > On Tue, Sep 24, 2013 at 6:20 PM, Stephen Chang <stchang at ccs.neu.edu>
> wrote:
> >>
> >> You need (require (for-syntax syntax/parse)) because you are using it
> >> inside a define-syntax.
> >>
> >> On Sep 24, 2013 11:56 AM, "Konrad Hinsen" <konrad.hinsen at fastmail.net>
> >> wrote:
> >>>
> >>> Hi everyone,
> >>>
> >>> I am trying to learn about syntax-parse, starting with the introduction
> >>> of the "Syntax" documentation.
> >>>
> >>> Unfortunately, the very first example given for the use of syntax-parse
> >>> doesn't work in my Racket installation:
> >>>
> >>>    Welcome to Racket v5.90.0.9.
> >>>    racket@> (require syntax/parse)
> >>>    racket@> (define-syntax (mylet stx)
> >>>                 (syntax-parse stx
> >>>                   [(_ ([var-id rhs-expr] ...) body ...+)
> >>>                    #'((lambda (var-id ...) body ...) rhs-expr ...)]))
> >>>    stdin::277: _: wildcard not allowed as an expression
> >>>      in: (_ ((var-id rhs-expr) ...) body ...+)
> >>>      errortrace...:
> >>>      context...:
> >>>       try-next
> >>>
> >>>
> /Users/hinsen/Development/racket/pkgs/errortrace-pkgs/errortrace-lib/errortrace/errortrace-lib.rkt:480:4
> >>>
> >>> /Users/hinsen/Applications/Racket/collects/racket/private/misc.rkt:87:7
> >>>
> >>> I tried replacing the wildcard by "mylet", but that only leads to
> another
> >>> error
> >>> message:
> >>>
> >>>    racket@> (define-syntax (mylet stx)
> >>>                 (syntax-parse stx
> >>>                   [(mylet ([var-id rhs-expr] ...) body ...+)
> >>>                    #'((lambda (var-id ...) body ...) rhs-expr ...)]))
> >>>    stdin::842: ...: ellipses not allowed as an expression
> >>>      in: ...
> >>>      errortrace...:
> >>>      context...:
> >>>       try-next
> >>>
> >>>
> /Users/hinsen/Development/racket/pkgs/errortrace-pkgs/errortrace-lib/errortrace/errortrace-lib.rkt:480:4
> >>>
> >>> /Users/hinsen/Applications/Racket/collects/racket/private/misc.rkt:87:7
> >>>
> >>> Am I doing something wrong here? Or are the examples obsolete?
> >>>
> >>> Konrad.
> >>> ____________________
> >>>   Racket Users list:
> >>>   http://lists.racket-lang.org/users
> >>
> >>
> >> ____________________
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> >>
> >
> >
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> >
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