[gambit-list] C Embedding question
Marc Feeley
feeley at iro.umontreal.ca
Thu Jan 29 10:56:57 EST 2009
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
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