I think Robby was confused by your example (which is understandable).
The `expand` function does not splice any differently than `compile`,
so `compile` behaves the same as `expand` in your example:
> (eval (compile #'(begin
(define-syntax (foo stx)
(displayln "hello")
#'5)
foo)))
foo: undefined;
cannot reference undefined identifier
context...:
/Users/mflatt/plt/racket/collects/racket/private/misc.rkt:87:7
> (compile #'(begin
(define-syntax (foo stx)
(displayln "goodbye")
#'5)
foo))
hello
#~....
I think Robby was just confused by your example, because he's used to
starting with a fresh REPL. :)
At Mon, 21 Dec 2015 22:16:44 -0700, Leif Andersen wrote:
> Wait, now I'm even more confused. If expand does the splicing and
> compile time evals song and dance, why do we need a separate function
> for:
>
> expand-syntax-top-level-with-compile-time-evals
>
> ?
>
> ~Leif Andersen
>
>
> On Mon, Dec 21, 2015 at 9:48 PM, Robby Findler
> <ro...@eecs.northwestern.edu> wrote:
> > I believe that's because expand does the splicing dance, but compile
> > doesn't (which is why you need the funny-named function ... "need" is
> > perhaps a poor choice of words here :).
> >
> > Robby
> >
> >
> > On Mon, Dec 21, 2015 at 10:30 PM, Leif Andersen <l...@leifandersen.net>
> wrote:
> >> Ah, that's a good question. One that I don't really know the answer
> >> too, because when I do:
> >>
> >>> (compile #'(begin
> >> (define-syntax (foo stx)
> >> (displayln "hello")
> >> #'5)
> >> foo))
> >>
> >> I get back the compiled object. Also foo is not displayed. And when I do:
> >>
> >> > (eval (compile #'(begin
> >> (define-syntax (foo stx)
> >> (displayln "hello")
> >> #'5)
> >> foo)))
> >>
> >> I get the error:
> >>
> >> foo: undefined;
> >> cannot reference an identifier before its definition
> >>
> >> But, when I do:
> >>
> >>> (expand #'(begin
> >> (define-syntax (foo stx)
> >> (displayln "hello")
> >> #'5)
> >> foo))
> >>
> >> It displays 'hello' to the console. And expands to what I would expect it
> too.
> >>
> >> ~Leif Andersen
> >>
> >>
> >> On Mon, Dec 21, 2015 at 9:15 PM, Alex Knauth <alexan...@knauth.org> wrote:
> >>>
> >>>> On Dec 21, 2015, at 10:53 PM, Leif Andersen <l...@leifandersen.net>
> >>>> wrote:
> >>>
> >>>> But `compile` is not supposed to evaluate any code, it just compiles
> >>>> it. Which is why it fails to compile that code. But if you interleave
> >>>> it with evals, it will run the require code, which gives the phase
> >>>> level 2 code some meaning.
> >>>
> >>> I understand that `compile` isn't supposed to evaluate any _runtime_
> >>> code,
> but I thought it had to evaluate the compile-time code for it to compile the
> program?
> >>>
> >>> Am I misunderstanding what `compile` is supposed to do? Or what
> compile-time code is, or?
> >>>
> >>>> Does that make any sense, or was it too rambly.
> >>>>
> >>>> ~Leif Andersen
> >>>>
> >>>>
> >>>> On Mon, Dec 21, 2015 at 8:24 PM, Alex Knauth <alexan...@knauth.org>
> >>>> wrote:
> >>>>> I get that `compile` doesn't evaluate the require form, but why doesn't
> it evaluate what's needed for compile time? I thought that was the reason for
> needing require as a macro instead of a function. Or am I getting the purpose
> of compile wrong?
> >>>>>
> >>>>> Alex Knauth
> >>>>>
> >>>>>> On Dec 21, 2015, at 7:47 PM, Matthew Flatt <mfl...@cs.utah.edu> wrote:
> >>>>>>
> >>>>>> In the REPL, `begin` splices at the granularity of expansion and
> >>>>>> evaluation. That is, the first of the two forms grouped by `begin` is
> >>>>>> compiled and evaluated, and only afterward the second one is compiled
> >>>>>> and evaluated.
> >>>>>>
> >>>>>> The `compile` function can't do that, because it's only supposed to
> >>>>>> compile -- not evaluate.
> >>>>>>
> >>>>>> The `syntax/toplevel` library provides
> >>>>>>
> >>>>>> expand-syntax-top-level-with-compile-time-evals
> >>>>>>
> >>>>>> as an intermediate point between those: it pulls apart `begin` and
> >>>>>> `expands` (which is the interesting part of `compile`) the forms in
> >>>>>> sequence, but it evaluates only compile-time parts of the given forms.
> >>>>>> That works for many cases, including your example.
> >>>>>>
> >>>>>> At Mon, 21 Dec 2015 17:35:22 -0700, Leif Andersen wrote:
> >>>>>>> So, I was under the impression that the REPL was the toplevel (unless
> >>>>>>> you entered a module context or something like that). But I just had
> >>>>>>> something challenge that assumption and so now I'm a bit confused.
> >>>>>>>
> >>>>>>> I have the following top level program:
> >>>>>>>
> >>>>>>> (begin
> >>>>>>> (require (for-meta 1 racket)
> >>>>>>> (for-meta 2 racket))
> >>>>>>> (begin-for-syntax
> >>>>>>> (begin-for-syntax
> >>>>>>> (define x 5))))
> >>>>>>>
> >>>>>>> When I run this top level program in the REPL, it works just fine. And
> >>>>>>> I can even reference x in later evaluations. (Provided I'm at the
> >>>>>>> meta-level of 2).
> >>>>>>>
> >>>>>>> However, when I pass this top level program into compile like so:
> >>>>>>> http://pasterack.org/pastes/38556
> >>>>>>>
> >>>>>>> (compile #'(begin
> >>>>>>> (require (for-meta 1 racket)
> >>>>>>> (for-meta 2 racket))
> >>>>>>> (begin-for-syntax
> >>>>>>> (begin-for-syntax
> >>>>>>> (define x 5)))))
> >>>>>>>
> >>>>>>>
> >>>>>>> I get the following error:
> >>>>>>>
> >>>>>>> define: unbound identifier at phase 2;
> >>>>>>> also, no #%app syntax transformer is bound in: define
> >>>>>>>
> >>>>>>> Can someone give me the reason (or at least some intuition) as to why
> >>>>>>> this works in the repl, but not at the top level?
> >>>>>>>
> >>>>>>> Thank you.
> >>>>>>>
> >>>>>>> ~Leif Andersen
> >>>>>>>
> >>>>>>> --
> >>>>>>> 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+unsubscr...@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.
> >>>>>> To unsubscribe from this group and stop receiving emails from it, send
> an email to racket-users+unsubscr...@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.
> >> To unsubscribe from this group and stop receiving emails from it, send an
> email to racket-users+unsubscr...@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.
To unsubscribe from this group and stop receiving emails from it, send an email
to racket-users+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
