Re: weird macro params issue

On Thu, May 22, 2008 at 3:28 PM, Attila Szegedi <[email protected]> wrote:
> On 2008.05.22., at 15:10, Tim Diggins wrote:
>
>> I hope you're not arguing that character count is more important than
>> understandability / readability / learnability.
>
> I'm not. As a matter of fact, to this day I prefer the old existence
> built-ins "?default" and "?exists" for similar reasons I prefer Java
> "extends" to C# ":" :-)
> I don't feel that <#macro m a b=a> impacts understandability or
> readability. To me,
>
> <#macro a b!>
>   <#if !b??>
>     <#local b=a/>
>   </#if>
> </#macro>
>
> would, honestly, be less understandable IMHO. The b=a doesn't
> introduce any new syntax - it's your good ol' defaulted argument, the
> only novelty is it's defaulting to value of another argument, which is
> also visually located near it, so I don't believe it makes
> understanding the meaning too daunting.

Actually, I just realized something.

Independently of whether we support this particular thing, our
semantics are quite different from Python semantics. In python, the
example I gave that failed:

def foo(x, y=x) :

Basically it fails because the default values in python are values.
They must be constant values that can be calculated when you define
the function.

FreeMarker default values (in 2.4 also) are not actually values, they
are expressions. (Of course, an expression that evaluates to a
constant value is very often used.)

So I guess the "what would Guido do" argument is kind of weak because
we're already so far away. It would seem then that if the default
values in a macro definition can be expressions (later evaluated on
invocation) that this use case is consistent with that.

So I guess my view is shifting on this. I honestly had the distinct
impression that you were implementing this basically because it could
be done, which of course made me nervous. The whole multipass thing
for tricky cases might be unnecessary, and it might be better just to
scan straightforwardly left to right as Felix suggested. Though, if
you are implementing it, you can do it as you want as far as I'm
concerned.

JR

>
> Attila.
>
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