On 29-Jan-09, at 10:38 AM, Alex Ryu wrote:
(c-define (evaluate str) (char-string) bool "evaluate" "extern" (catch-all-errors (lambda () (eval (read-from-string (string-append "\" str ";"))))))
This will use Gambit's SIX parser (Scheme infix syntax extension).
This is untested code.
Marc
Thank you for the advice and sorry for being obtuse. Do I not need a write-to-string before the eval?
The C "evaluate" function that you have in your example is returning a Boolean value. So you want the Scheme "evaluate" function to return a Boolean value (i.e. #f is false, and anything else is true). The c- define I suggested, i.e.
(c-define (evaluate str) (char-string) bool "evaluate" "extern" ...)
defines the return type to be "bool", so the FFI interface will convert the Scheme value that is returned by the Scheme "eval" into a C "bool" value (which by the way is the "int" type in C, and the "bool" type in C++).
A call to write-to-string would only be useful if you wanted your C "evaluate" function to return a string with the external representation of the value returned by "eval". The c-define would be:
(c-define (evaluate str) (char-string) char-string "evaluate" "extern" ...)
You could do that but then in your C code you would have to check if the string returned by "evaluate" is "#f", which is clumsy if you are really calling "evaluate" for testing conditions.
Marc