Oh right. Sorry for the confusion! Robby
On Tuesday, December 22, 2015, Matthew Flatt <mfl...@cs.utah.edu> wrote: > 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 <javascript:;>> 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 > <javascript:;>> > > 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 > <javascript:;>> wrote: > > >>> > > >>>> On Dec 21, 2015, at 10:53 PM, Leif Andersen <l...@leifandersen.net > <javascript:;>> 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 > <javascript:;>> 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 > <javascript:;>> 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 > <javascript:;>. > > >>>>>>> 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 <javascript:;>. > > >>>>>> 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 <javascript:;>. > > >> 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 <javascript:;>. > 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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