* Anton Rolls <[EMAIL PROTECTED]> [051001 15:06]:
> Consider that the above line might be written by you in a script like this:
>
> cd
> ;
> ; some intervening comments like this might make the line above
> ; and the line below look completely unrelated.
> ;
> do [{some long code that returns a value} 10 + 2]
>
> which has the same output:
>
> change-dir to 12
>
> A solution is to wrap in parens like this:
>
> >> (cd) do [{some long code that returns a value} 10 + 2]
> %/D/Anton/Dev/Rebol/View/
> == 12
>
> But it doesn't help you to remember whether you need the parens or not.
> If you forget, you can have a confusing bug for while.
> So you always wrap in parens (no thought required), or only use parens when
> there can be a value afterwards (requires your careful attention).
>
> It just makes things complicated, so that's why we generally avoid
> accepting unset! in function arguments.
Good advice. In my case it simplifies things to use a function like
this, but my approach would be to use it only inside of
well-thought-out subroutines.
With your advice well in mind. :-)
Another approach could be best illustrated by some pythonesque pseudo-code:
as in
try:
t: print "this will generate an error with an id of: 'need-value"
except NeedValueError: ## python traps only the error you want to
## trapped
return default-value
(I love rebol, but python has some valuable error-trapping classes)
;; so we could do this with rebol:
main: func[][
t: print "hello"
]
dump-error: func[obj[object!]][
if obj/id = 'need-value[
print "handling a no value error"
return ""
]
]
;;
=========================================================================================
application: [; execution block
print <pre>
main
]
;;======================================================================================================
except: [dump-error disarm err ]
if error? set/any 'err try application except
--
Tim Johnson <[EMAIL PROTECTED]>
http://www.alaska-internet-solutions.com
--
To unsubscribe from the list, just send an email to
lists at rebol.com with unsubscribe as the subject.
