On 27-Jun-09, at 10:32 PM, lowly coder wrote:

Is there a way to overload pp for define-types? (maybe some undocumented arg in (define-type ...) ?) I would like to change how they're printed. Also, can I override existing ones, like f32vector? When I have something that's 1000 f32's, I'd prefer an output of <#f32vector ...> rather than all 1000 elems.

Thanks!

(If not, I'll just define a separate command like pp2 and use that instead, but overloading pp somehow seems more elegant).

This can be done by redefining the ##wr variable which is normally set to ##default-wr. The first parameter of the procedure is the "write environment", which contains the port to write to, and the second parameter is the object to write.

Here's a quick example:

(define-type person name gender)

(set! ##wr (lambda (we obj) (if (person? obj) (begin (##wr-str we "{PERSON:") (##wr-str we " name=") (##wr we (person-name obj)) (##wr-str we " gender=") (##wr we (person-gender obj)) (##wr-str we "}")) (##default-wr we obj)))) ;; otherwise use default writer

(pp (make-person "marc" 'male)) ;; prints: {PERSON: name="marc" gender=male}

If you want to "pretty-print" the objects, follow the model of the procedure ##wr-structure defined in lib/_io.scm .

Marc