[REBOL] Re: A question of function interface design
From: volker::nitsch::gmail::com at: 19-Jan-2005 16:33
On Wed, 19 Jan 2005 19:17:54 +0800, PeterWAWood <[pwawood--mango--net--my]> wrote:
> I have started to question whether it is best to use Rebol's automatic type
> checking of parameters or not when designing functions.
>
> If the type checking is used, calling a function with an incorrect type of
> value causes a script error, eg:
>
> >> a: func [b [date!]] [print b]
> >> a 12345
> ** Script Error: a expected b argument of type: date
> ** Near: a 12345
>
> However, if you don't use the built-in type checking, you can return a none!
> value and give the caller the option (and responsibility) to deal with the
> situation, eg:
>
> >> a: func [b] [if type? b <> date! [return none]]
> >> a 12345
> == none
>
> Given that Rebol is not strongly typed, is the second of these "idioms" the
> more appropriate?
>
No.
1) its longer. if it would be good, we would have a shortcut :)
2) this func [b [date!]] is the shortcut.
3) there are two types of fails: such which regulary happens(none!),
and such which should never happen(error!).
Thats why 'find returns none: often we want to know if something exists.
'read throws an error when file is missing: we rarely are prepared to
deal with 'none instead of file-content.
This keeps the code shorter, avoids continuing with broken data, and
is simply smart: "hey coder, you forgot a file ;)".
If the function-coder specifies a certain type, it means something.
And passing something else is an coding-error. And the computer should
be helpfull to do the right thing: decide if coder made error or did
expect failing.
In statically typing he does that conservative: if it could be wrong,
it is wrong. in dynamically typing he flags only when he is really
sure its wrong: at runtime with real data. but he checks.
there is always 'attempt if you really may to call with wrong args: if
attempt[to-integer ask "only numbers"][print "hohoho"] ;)
> Regards
>
> Peter
>
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--
-Volker
Any problem in computer science can be solved with another layer of
indirection. But that usually will create another problem.
David
Wheeler
