Bytecode problem with fxvector inside a macro

[Dmitry Pavlov]

Hello,

I would like to report something that I see as
inconsistent behavior of the bytecode compiler.
The following short program (an artificial minimal
reproducible example) works at first, but fails
after raco make. My OS is Linux.



$ cat one.rkt
#lang racket

(require (for-syntax syntax/parse racket/fixnum))

(define-syntax (macro stx)
(syntax-parse stx
(({~literal macro})
(let ((v (fxvector 5)))
(with-syntax ((v v))
(quasisyntax/loc stx
(begin
(define v-name v)
'OK)))))))

(macro)

$ racket one.rkt
'OK

$ raco make one.rkt

$ racket one.rkt
read: bad syntax `#fx'
in: compiled/one_rkt.zo
context...:
read-linklet-or-directory
read-dispatch
read
default-load-handler
standard-module-name-resolver
module-path-index-resolve
[repeats 1 more time]
module-declared?


$ racket -v
Welcome to Racket v7.2.


Best regards,

Dmitry

[Matthew Flatt]

The intended error here is "cannot marshal value that is embedded in
compiled code" at `raco make` time, because fxvectors are not supported
as literals. I'll fix the bytecode writer to check for this case.

Meanwhile, the fact that non-literal values can be coerced to syntax
(as long as they don't have to be marshaled) is troublesome, but it's
useful enough in interactive situations that we haven't yet committed
to closing the loophole.

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[Dmitry Pavlov]

Matthew,

> The intended error here is "cannot marshal value that is embedded in
> compiled code" at `raco make` time, because fxvectors are not supported
> as literals. I'll fix the bytecode writer to check for this case.

OK, thank you. What would you recommend, though, to users who want fxvectors (of "static" kind) to be generated by macros?
Populating fxvectors in runtime will be a loss of performance, maybe not critical, but noticeable.

Best regards,

Dmitry

[Dmitry Pavlov]

Ah, I see

#lang racket

(require (for-syntax syntax/parse))
(require  racket/fixnum)

(define-syntax (macro stx)
  (syntax-parse stx
    (({~literal macro})

     (quasisyntax/loc stx
       (begin
         (define v-name (fxvector 5))
         'OK)))))

(macro)


So I should put fxvector non-literals inside the syntax, and everything will be fine.


Best regards,

Dmitry

[Matthew Flatt]

Yes. Or if the macro is used in a potentially nested expression context
and you want to make sure that the fxvector is created once, you can
use `syntax-local-lift-expression`.