bug#52218: Unable to define more than one R7RS library per file

bug#52218: Unable to define more than one R7RS library per file

[Sam Lee via Bug reports for GUILE, GNU's Ubiquitous Extension Language]

Guile is unable to handle more than one define-library per file. For
example, this is "mylibs.sld", which contains two define-library:

(define-library (example mylib)
  (import (scheme base))
  (export f)
  (begin
    (define (f x)
      (+ x 1))))

(define-library (example main)
  (import (scheme base)
          (scheme write)
          (example mylib))
  (export main)
  (begin
    (define (main)
      (display "The answer is: ")
      (display (f 1))
      (newline))))


When loading this file into Guile using "guile -l mylibs.sld", or by
using (load "mylibs.sld"), Guile will show this error:

;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
;;;       or pass the --no-auto-compile argument to disable.
;;; compiling /home/user/mylibs.sld
;;; WARNING: compilation of /home/user/mylibs.sld failed:
;;; Syntax error:
;;; unknown location: definition in expression context, where definitions are not allowed, in form (define (main) (display "The answer is: ") (display (f 1)) (newline))
ice-9/psyntax.scm:2794:12: In procedure syntax-violation:
Syntax error:
/home/user/mylibs.sld:14:4: definition in expression context, where definitions are not allowed, in form (define (main) (display "The answer is: ") (display (f 1)) (newline))


The error is always caused by the second define-library. Apparently,
Guile no longer understands that define-library is a special form by the
time the second define-library is evaluated. Is it not possible to
define two R7RS libraries in the same file?

Guile version: 3.0.7

bug#52218: Unable to define more than one R7RS library per file

[Linus Björnstam]

Hi Sam!

I am not a maintainer , nor a very proficient guile hacker, but I do have some input.

This is in line with the limitations of guile's R6RS implementation. I think this is a long standing, low priority bug. It has to do with the expansion of library (or define-library in this case) not properly resetting the current module. 

In the manual there is a section called "R6RS incompatibilities" that mentions this. Maybe an "R7RS incompatibilities" should be added.


Best regards
  Linus Björnstam

On Wed, 1 Dec 2021, at 08:45, Sam Lee via Bug reports for GUILE, GNU's Ubiquitous Extension Language wrote:
> Guile is unable to handle more than one define-library per file. For
> example, this is "mylibs.sld", which contains two define-library:
>
> (define-library (example mylib)
>   (import (scheme base))
>   (export f)
>   (begin
>     (define (f x)
>       (+ x 1))))
>
> (define-library (example main)
>   (import (scheme base)
>           (scheme write)
>           (example mylib))
>   (export main)
>   (begin
>     (define (main)
>       (display "The answer is: ")
>       (display (f 1))
>       (newline))))
>
>
> When loading this file into Guile using "guile -l mylibs.sld", or by
> using (load "mylibs.sld"), Guile will show this error:
>
> ;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
> ;;;       or pass the --no-auto-compile argument to disable.
> ;;; compiling /home/user/mylibs.sld
> ;;; WARNING: compilation of /home/user/mylibs.sld failed:
> ;;; Syntax error:
> ;;; unknown location: definition in expression context, where 
> definitions are not allowed, in form (define (main) (display "The 
> answer is: ") (display (f 1)) (newline))
> ice-9/psyntax.scm:2794:12: In procedure syntax-violation:
> Syntax error:
> /home/user/mylibs.sld:14:4: definition in expression context, where 
> definitions are not allowed, in form (define (main) (display "The 
> answer is: ") (display (f 1)) (newline))
>
>
> The error is always caused by the second define-library. Apparently,
> Guile no longer understands that define-library is a special form by the
> time the second define-library is evaluated. Is it not possible to
> define two R7RS libraries in the same file?
>
> Guile version: 3.0.7

bug#52218: Unable to define more than one R7RS library per file

[Sam Lee via Bug reports for GUILE, GNU's Ubiquitous Extension Language]

On 2021-12-01 11:00 +0100, Linus Björnstam wrote:
> This is in line with the limitations of guile's R6RS implementation. I
> think this is a long standing, low priority bug. It has to do with the
> expansion of library (or define-library in this case) not properly
> resetting the current module.
>
> In the manual there is a section called "R6RS incompatibilities" that
> mentions this. Maybe an "R7RS incompatibilities" should be added.

Hi Linus,

There already exist a page in the manual about "Incompatibilities with
the R7RS" [1]. Perhaps a paragraph similar to that found in the R6RS
incompatibilities page should be added to the R7RS incompatibilities
page. Something like this:

"Multiple @code{define-library} forms in one file are not yet supported.
This is because the expansion of @code{define-library} sets the current
module, but does not restore it.  This is a bug."

[1]: https://www.gnu.org/software/guile/manual/html_node/R7RS-Incompatibilities.html

bug#52218: Unable to define more than one R7RS library per file

[Linus Björnstam]

It is the same bug. The r7rs define-library expands to a r6rs library, which expands to a guile module form that lacks support for multiple libraries. The solution would probably include a non-trivial (but probably not very big) change to guile's module system.

First you would have to save and restore the current module before and after a module definition (maybe in save-module-excursion?). Then I would separate the library form the guile library form (since that doesn't encapsulate the body), by expanding it directly to the lower level module forms.

I might give it a shot.

-- 
  Linus Björnstam

On Thu, 2 Dec 2021, at 03:55, Sam Lee wrote:
> On 2021-12-01 11:00 +0100, Linus Björnstam wrote:
>> This is in line with the limitations of guile's R6RS implementation. I
>> think this is a long standing, low priority bug. It has to do with the
>> expansion of library (or define-library in this case) not properly
>> resetting the current module.
>>
>> In the manual there is a section called "R6RS incompatibilities" that
>> mentions this. Maybe an "R7RS incompatibilities" should be added.
>
> Hi Linus,
>
> There already exist a page in the manual about "Incompatibilities with
> the R7RS" [1]. Perhaps a paragraph similar to that found in the R6RS
> incompatibilities page should be added to the R7RS incompatibilities
> page. Something like this:
>
> "Multiple @code{define-library} forms in one file are not yet supported.
> This is because the expansion of @code{define-library} sets the current
> module, but does not restore it.  This is a bug."
>
> [1]: 
> https://www.gnu.org/software/guile/manual/html_node/R7RS-Incompatibilities.html