Load external scm files

Load external scm files

[Lovis Suchmann]

Hello everyone,

I'm working with Guile Scheme (with the LilyPond music engraver 
software, if someone knows this), and atm I have the problem that I 
would like to load an external scheme file in the current environment, like

; external.scm
(define x 3)

; main.scm
(define (make-test-function)
   (load "external.scm")
   (lambda () x))
(define test-function (make-test-function))
(display (test-function)) ; => 3
(display x) ; => should create an error because x should not be accessible

I tried but failed with this and found out it is because 'load' always 
uses the top-level environment. Is there another way to load a file in 
the current context? Like, in the way as if I just copy-and-pasted the 
contents of the file at this exact position? Or do you have any other 
suggestions?

Thanks in advance. :)

Lovis

Re: Load external scm files

[Ralf Mattes]

On Wed, Dec 04, 2013 at 02:52:10PM +0100, Panicz Maciej Godek wrote:
> This looks like a job for a macro!
> 
> (define-macro (define-test-function)
>   `(define (test-function)
>      ,(load "external.scm")
>      x))
> 
> (define-test-function)
> 
> (test-function)
> ; ==> 3

No  - this doesn't solve the OP's question.
Even with your macro, x is still defined in 
the toplevel. Try this:

(display (test-function)) 
(display x)  ; visible from the toplevel
(set! x 42)
(display (test-function)) ; Outsch!

Cheers, Ralf Mattes

Re: Load external scm files

[Panicz Maciej Godek]

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This looks like a job for a macro!

(define-macro (define-test-function)
  `(define (test-function)
     ,(load "external.scm")
     x))

(define-test-function)

(test-function)
; ==> 3

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Re: Load external scm files

[Panicz Maciej Godek]

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Oh yes, you're right -- it's because of the behaviour of "load".
However, this should solve the problem:
(define-macro (define-test-function)
  `(define (test-function)
     ,(with-input-from-file "external.scm" read)
     x))

(note however that it would load only the first sexp from
"external.scm", but I think that it should be a sufficient hint)

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Re: Load external scm files

[dsmich]

---- Lovis Suchmann <panlovis@aol.com> wrote: 
> Hello everyone,
> 
> I'm working with Guile Scheme (with the LilyPond music engraver 
> software, if someone knows this), and atm I have the problem that I 
> would like to load an external scheme file in the current environment, like
> 
> ; external.scm
> (define x 3)
> 
> ; main.scm
> (define (make-test-function)
>    (load "external.scm")
>    (lambda () x))
> (define test-function (make-test-function))
> (display (test-function)) ; => 3
> (display x) ; => should create an error because x should not be accessible
> 
> I tried but failed with this and found out it is because 'load' always 
> uses the top-level environment. Is there another way to load a file in 
> the current context? Like, in the way as if I just copy-and-pasted the 
> contents of the file at this exact position? Or do you have any other 
> suggestions?

Sounds like a job for include:  http://www.gnu.org/software/guile/manual/html_node/Local-Inclusion.html#index-include

-Dale

Re: Load external scm files

[Ralf Mattes]

On Wed, Dec 04, 2013 at 12:04:34PM -0500, dsmich@roadrunner.com wrote:
> 
> Sounds like a job for include:  http://www.gnu.org/software/guile/manual/html_node/Local-Inclusion.html#index-include
> 

Yes, except Lilypond's main branch strill uses guile-1.8 and that doesn't know 'include.
I think at this point it might be a good idea to ask the OP what problem he tries to solve.
Writing scheme code into a file  that gets spliced into a function definition sounds like
a kludge to me. If visibility/encapsulation is the goal, maybe a module is the better
solution (plus, maybe some syntactic sugar to hide guile's module system: (define-plugin ...)
which would expand into (define-module ...) and (use-plugin ...) that would expand into
a (use-modules ...) with an appropriate symbol-renamer that transforms a module name
(foo bar baz) into foo.bar.baz.exported-symbol ...)

Cheers RalfD
 
> -Dale
> 
>