why is:
(load "t1.scm") (define x 20)
valid, where as:
(define-macro (foo) (load "t1.scm") (define x 20))
result in a ill-placed define error?
This is not a problem specific to macros, the same error would happen if you did
(define (foo) (load "t1.scm") (define x 20))
That would fail, as would
(lambda () (load "t1.scm") (define x 20))
, and
(lambda () (+ 1 1) (define x 20))
. load is just a "normal" function, whereas define is a special form, and it has to be in the beginning of a scope, before any function calls are made.
I think of it as if Gambit internally converts defines within scopes to letrecs, like
(lambda () (define x 1) (define y 2) (+ x y)) => (lambda () (letrec ((x 1) (x 2)) (+ x y)))
Given that definition, your code above doesn't really make any sense. You could write
(lambda () (load "t1.scm") (let () (define x 20)))
or
(lambda () (define x #f) (load "t1.scm") (set! x 20)))
depending on what you want.
/Per