But Chez Scheme's FFI, while very powerful and simple, simply doesn't have a specific way to manage error reports coming back. How do you get access to the errno? Is your method thread safe? The calling context switches back and forth between Chez Scheme and foreign code could very well cause errno to be overwritten. How do you handle this?
Well, let's go into some Chez Scheme black magic. Beware! This is unsafe and dangerous if you don't know what you are doing! Don't try this at home kids. ;-)
(define errno (let ([errno-ent (#%$foreign-entry "errno")]) (lambda () (foreign-ref 'int errno-ent 0)))) (define errno-message (let ([$strerror (foreign-procedure "strerror" (fixnum) string)]) (lambda (num) ($strerror num)))) (define (call-with-errno thunk receiver) (call-with-values (lambda () (critical-section (let ([v (thunk)]) (values v (errno))))) receiver))
Alter to taste.