Portable load/include of define-syntax in R5RS Scheme?

I'm trying to write something that works in both DrRacket/plt-r5rs and Gambit/gsi.

The problem I'm having is that (load "foo.scm") in Gambit does not load define-syntax-blocks. Using (include "foo.scm") in Gambit works, but of course results in a syntax error in DrRacket.

Is there any way to solve this so that I can write portable R5RS code?

Things I've tried:

• Redefining (include "foo.scm") to (load "foo.scm") and vice versa. Problem: Illegal to redefine macros in Gambit.
• Wrapping said redefinitions in an (if gambit ...). Problem: Illegal to put define inside if(unless inside another define).
• Passing string with filename to an include in the library file instead. Problem: Includes in Gambit seem to happen before interpretation starts.

It's very hard to write a module that's compatible with both Gambit and Racket.

There are indeed ways you can test for a specific implementation and define things conditionally. There are, in fact, two systems for doing this: SRFI 0 and SRFI 7. Most implementations support one or the other. Not very many support both.

Gambit supports SRFI 0. Racket supports SRFI 7.