Am 17.11.2013 03:02, schrieb David A. Wheeler:
> I've tweaked the "readable" code to address some of the portability issues
> that Joerg Wittenberger noted. It should now be easier to port the code to
> other Schemes.
>
> The main code now uses R6RS/R7RS exception syntax and makes a call to a
> special init-sweet.
> The guile-specific code now "implements" R6RS/R7RS exception syntax, and its
> version of init-sweet calls the guile-specific "debug-set!. That eliminates
> those
> guile-specific portions from the main code line. Implementations that
> support R6RS/R7RS
> exception syntax and need no special initialization should now work unchanged.
>
> Joerg: I hope that helps. This version works on guile.
Does it? Then either guile has an (eq? eq eq?) evaluate to true or the
exception handler was never invoked. That is: I would guess.
My problem with this corner of the code is that I don't understand what
it is supposed to do.
(define (t-expr-catch port)
(init-sweet)
(guard
(exception
((eq exception 'readable)
(read-to-unindented-line port) (t-expr-catch port)))
(t-expr port)))
1. I would believe that this ought to be ((eq? exception 'readable) ...)
Note thee missing question mark.
2. The exception handler will somehow catch all exceptions from
read-error, correct? Then it handles them by ignoring the error input
and some following text, still correct? Somehow the error will only
appear on the error port (which is something I'd have to handle somehow
special anyway, since when I'm running this in a server, it will only
garble my error log file.
But also the guard implementation itself looks suspicious to me:
(define-syntax guard
(syntax-rules ()
((guard
(exception ((eq exception2 value) run-when-true ...))
body)
(catch value
(lambda () body)
(lambda (key . args) run-when-true ...)))))
Besides that it again relies on my assumption that guile must have eq as
alias to eq?, I don't see where the identifier exception2 becomes bound.
/Jörg
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