2.7 Compilation

By default, Gauche reads toplevel Scheme forms one at a time, compile it immediately to intermediate form and execute it on the VM. As long as you use Gauche interactively, it looks like an interpreter. (There’s an experimental ahead-of-time compiler as well. See HOWTO-precompile.txt if you want to give a try.)

The fact that we have separate compilation/execution phase, even interleaved, may lead a subtle surprise if you think Gauche as an interpreter. Here’s a few points to keep in mind:

load is done at run time.

load is a procedure in Gauche, therefore evaluated at run time. If the loaded program defines a macro, which is available for the compiler after the toplevel form containing load is evaluated. So, suppose foo.scm defines a macro foo, and you use the macro like this:

;; in “foo.scm”
(define-syntax foo
  (syntax-rules () ((_ arg) (quote arg))))

;; in your program
(begin (load "foo") (foo (1 2 3)))
  ⇒ error, bad procedure: ‘1’

(load "foo")
(foo (1 2 3)) ⇒ '(1 2 3)

The (begin (load ...)) form fails, because the compiler doesn’t know foo is a special form at the compilation time and compiles (1 2 3) as if it is a normal procedure call. The latter example works, however, since the execution of the toplevel form (load "foo") is done before (foo (1 2 3)) is compiled.

To avoid this kind of subtleties, use require or use to load a program fragments. Those are recognized by the compiler.

require is done at compile time

On the other hand, since require and use is recognized by the compiler, the specified file is loaded even if the form is in the conditional expression. If you really need to load a file on certain condition, use load or do dispatch in macro (e.g. cond-expand form (see Feature conditional).)