Anonymous user
Use another language to call a function: Difference between revisions
Use another language to call a function (view source)
Revision as of 10:39, 5 May 2015
, 9 years ago→{{header|Racket}}: New Racket solution
(Nimrod -> Nim) |
(→{{header|Racket}}: New Racket solution) |
||
Line 817:
$
</lang>
=={{header|Racket}}==
Since this problem is presented as the inverse to [[Call foreign language function]], I've focused on just demonstrating a callback from C into Racket, instead of showing how to [http://docs.racket-lang.org/inside/embedding.html embed the whole Racket runtime into C].
Starting with the given C code, modify it so that <tt>Query</tt> is a variable instead of an external:
<lang C>
typedef int strfun (char * Data, size_t * Length);
strfun *Query = NULL;
</lang>
The rest of the C code is left as-is. Compile it into a dynamic library, then run the following Racket code:
<lang racket>
#lang racket
(require ffi/unsafe)
(define xlib (ffi-lib "./x.so"))
(set-ffi-obj! "Query" xlib (_fun _pointer _pointer -> _bool)
(λ(bs len)
(define out #"Here I am")
(let ([bs (make-sized-byte-string bs (ptr-ref len _int))])
(and ((bytes-length out) . <= . (bytes-length bs))
(begin (bytes-copy! bs 0 out)
(ptr-set! len _int (bytes-length out))
#t)))))
((get-ffi-obj "main" xlib (_fun _int (_list i _bytes) -> _void))
0 '())
</lang>
Note that this code is intentionally in a simple low-level form, for example, it sets the pointer directly instead of using a C function.
The output is the expected “<tt>Here I am</tt>” line.
=={{header|Tcl}}==
| |||