Re: [gambit-list] #ifdef equivalent in Scheme?

On 2013-04-16, at 4:43 PM, Ralph Moritz ralph.moeritz@outlook.com wrote:

I'm trying to get Black Hole trunk to run on Windows & need to compile different Scheme code depending on the target OS.

eg. On Unix-like OSes the following is ok:

(compile-file-to-target "/dev/null"
                        output: fn
                        options: options))

...but on Windows `/dev/null' needs to be replaced with `\\.\NUL'. In C I'd do something like:

#ifdef _WINDOWS /* or whatever */
# define NULLDEV "\\\\.\\NUL"
#else
# define NULLDEV "/dev/null"
#endif

Is there a Scheme equivalent to #ifdef et al? If the answer is `no' then please tell me what you'd do in this case?

The closest thing to #ifdef is (cond-expand ...). For example:

(cond-expand (gambit (define (arguments) (cdr (command-line)))) (else (define (arguments) '())))

However you can't test the host operating system that way. You could call (system-type) at run time to get some information on the host environment:

(system-type) => (i386 apple darwin12.3.0)

But to use this you will need to parse the last element of the list.

It may seem like a hack, but the most reliable way to detect different filesystems is to check the path separator character, which is \ on Windows and / on Unix:

(define windows? (char=? #\ (let ((cd (current-directory))) (string-ref cd (- (string-length cd) 1)))))

In Gambit, directories are guaranteed to end with the path separator character.

You could also use functions that are specific to Windows:

(define windows? (string=? (path-volume "c:") "c:"))

Who can come up with other ways? :-)

Marc