how far does eval go when module gets compiled?

how far does eval go when module gets compiled?

[Matt Wette]

When a module is compiled to generate a .go file is it possible to know (predict) what will be evaluated?

For example

(define-module (foo) #:export (bar))

(define bar (+ 3 4))

Is the “+” executed at compile time or at load time?

Matt

Re: how far does eval go when module gets compiled?

[Taylan Ulrich Bayırlı/Kammer]

Matt Wette <matthew.wette@verizon.net> writes:

> When a module is compiled to generate a .go file is it possible to know (predict) what will be evaluated?
>
> For example
>
> (define-module (foo) #:export (bar))
>
> (define bar (+ 3 4))
>
> Is the “+” executed at compile time or at load time?

Nothing is really evaluated during compilation.  (Not counting
optimization like partial evaluation.)

The "top-level" of a module is evaluated once when the module is loaded
into the run-time, whether it's in source form or a compiled .go.

So the "(+ 3 4)" in your example is (theoretically) evaluated when some
piece of code containing e.g. (use-modules (foo)) is executed, and the
module was not already loaded into the running Guile process.  (Although
due to optimization, that "(+ 3 4)" will probably be turned into 7 at
compile-time.)

Note that there is a macro called 'eval-when' which can let you
explicitly evaluate expressions at compile-time.

And of course, all macro procedures get evaluated at compile-time to
transform the compiled code as desired.

Hope that helps,
Taylan

Re: how far does eval go when module gets compiled?

[Ludovic Courtès]

taylanbayirli@gmail.com (Taylan Ulrich "Bayırlı/Kammer") skribis:

> So the "(+ 3 4)" in your example is (theoretically) evaluated when some
> piece of code containing e.g. (use-modules (foo)) is executed, and the
> module was not already loaded into the running Guile process.  (Although
> due to optimization, that "(+ 3 4)" will probably be turned into 7 at
> compile-time.)

Right:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> ,optimize (lambda (x) (+ 3 4))
$2 = (lambda (x) 7)
--8<---------------cut here---------------end--------------->8---

Ludo'.