(I've messed up with git send-email, the patch with this email is
at http://lists.gnu.org/archive/html/guile-devel/2017-02/msg00008.html).
Some objects have large printed representations and trying to print
them can kill the terminal. This is a serious problem when handling
e.g. big arrays.
For repl values there's (repl-default-option-set! 'print (lambda (val)
...)) which lets you override the default printing routine. But for
exceptions there's no equivalent. The default exception printers are
in (ice-9 boot-9) and are difficult to override. Besides, the format
of the exception output is often chosen by arguments to scm-error and
not by those printers.
The patch to master (ice-9 boot-9) lets you override the (format) used
internally by the exception printers. Then I rewrite the format string
in user code, see below. It's a bit hacky, maybe someone has a better
solution.
See also the other patch I've posted to the list to support arrays in
(truncated-print). The patches are independent, but they make each
other useful so to speak.
Regards
Daniel
(In the code below for .guile, replace [AT] by the at symbol).
; Truncate output on exceptions. Requires exception-format in ice-9/boot.scm.
; FIXME doesn't handle e.g. "x~~~s" -> "x~~~[AT]y"
(define (rewrite-fmt fmt)
(let loop ((f "") (b 0))
(let ((next (string-contains-ci fmt "~s" b)))
(if next
(loop
(if (or (zero? next) (not (char=? #\~ (string-ref fmt (- next 1)))))
(string-append f (substring fmt 0 next) "~[AT]y")
fmt)
(+ b next 2))
(string-append f (substring fmt b))))))
(when (defined? 'exception-format)
(set! exception-format
(lambda (port fmt . args)
(apply format port (rewrite-fmt fmt) args))))
