Just a follow up:

It is possible to do it with a cond-expand, as the gerbil compiler can detect when it is compiling with (not safe).
The contract check in the generated code would be at the function entry point and look like:
(cond-expand
 (gerbil-runtime-checks
  ...) ;; do checks and raise exception if the contract is violated
 (else))

When the compiler detects that it is in a safe context (absence of a local or prelude (not safe) declaration), then it
can emit a (define-cond-expand-feature|gerbil-runtime-checks|) for gsc, and compile in the contract checks.

This is a reasonably good solution, so there is no pressing need to add a construct to gambit that conditionally compiles based on declarations.

-- vyzo


On Tue, Nov 26, 2019 at 8:39 PM Dimitris Vyzovitis <vyzo@hackzen.org> wrote:
Is there a mechanism by which we can declare code to be eliminated when compiling with (declare (not safe))?
I haven't been able to find anything, and it would be very nice to have something like (when-declare (safe) stuff ...),
which would be eliminated in unsafe compilation.
The context is that I want to add a contract system to Gerbil, but I don't want the runtime checks to persist when
compiling with (not safe).

-- vyzo