Re: Fancy sub arg handling: ability to expand error message?
On Sat, Mar 28, 2015 at 5:43 PM, Tom Browder wrote: > Agree--looks like we need some of Damien Conways wonderful CPAN modules That should be "Damian Conway's" -Tom
Re: Fancy sub arg handling: ability to expand error message?
On Sat, Mar 28, 2015 at 2:53 PM, Moritz Lenz wrote:
> On 28.03.2015 12:27, Tom Browder wrote:
> > I like the subroutine arg handling in Perl 6. Is there any simple
> > way to attach a short error msg in place of or additive to the
> > default for, say, a missing arg?
>
> You can always use multi subs, and use a catch-all candidate which
> produces the error message.
>
> multi thingy($x) { $x + 42 }
> multi thingy(|c) { die "Must call &thingy with exactly one argument" }
Multis? I guess my mind went elsewhere:
sidhekin@purplehat[00:25:02]~$ cat > tom.p6
sub foo($x = (warn "&foo called without argument; using default (42)"; 42)
) {
$x + 42;
}
sub bar($x = (die "&bar called without argument; failing") ) {
$x + 42;
}
say foo(-2);
say foo();
say bar(-2);
say bar();
sidhekin@purplehat[00:25:21]~$ perl6 tom.p6
40
&foo called without argument; using default (42) in sub foo at tom.p6:1
84
40
&bar called without argument; failing
in sub bar at tom.p6:5
in block at tom.p6:12
sidhekin@purplehat[00:25:27]~$
Eirik
Re: Fancy sub arg handling: ability to expand error message?
On Mar 28, 2015 8:54 AM, "Moritz Lenz" wrote:
> On 28.03.2015 12:27, Tom Browder wrote:
> > I like the subroutine arg handling in Perl 6. Is there any simple
> > way to attach a short error msg in place of or additive to the
> > default for, say, a missing arg?
>
> You can always use multi subs, and use a catch-all candidate which
> produces the error message.
>
> multi thingy($x) { $x + 42 }
> multi thingy(|c) { die "Must call &thingy with exactly one argument" }
>
> Though IMHO that's usually not worth the trouble; you get the error
> message only for programming errors, not for user errors; and
> programmers should be able to understand the error message (or we need
> to improve the error messages, if that's not the case).
>
> Also it makes it harder for others to extend your API by providing
> additional multi candidates.
Agree--looks like we need some of Damien Conways wonderful CPAN modules
ported ASAP!
Cheers!
-Tom
Re: Fancy sub arg handling: ability to expand error message?
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Hi,
On 28.03.2015 12:27, Tom Browder wrote:
> I like the subroutine arg handling in Perl 6. Is there any simple
> way to attach a short error msg in place of or additive to the
> default for, say, a missing arg?
You can always use multi subs, and use a catch-all candidate which
produces the error message.
multi thingy($x) { $x + 42 }
multi thingy(|c) { die "Must call &thingy with exactly one argument" }
Though IMHO that's usually not worth the trouble; you get the error
message only for programming errors, not for user errors; and
programmers should be able to understand the error message (or we need
to improve the error messages, if that's not the case).
Also it makes it harder for others to extend your API by providing
additional multi candidates.
Cheers,
Moritz
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