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From Stefan Bodewig <bode...@apache.org>
Subject Re: Vote: <local> for 1.6
Date Thu, 23 Oct 2003 12:36:12 GMT
On Thu, 23 Oct 2003, peter reilly <peter.reilly@corvil.com> wrote:

> One example would be the way lisp does things.
> 
>   (let ((here (point))
>         (ignore-depth 0)
>         (tag-info context))
>     bla.. bla..
>   )

At least Emacs Lisp uses dynamic extent here,  i.e. with

(setq here bar)
(let ((here foo))
  (some-method))

the function some-method would see the value foo for 'here.

I'm not familiar enough with other Lisp dialects.  So if you want to
draw this parallel, <ant> would have to inherit the local shadows.
And <macrodef> would see the same problems (defmacro) has and we'd
have to introduce "uninterned symbols" to solve some issues,
(i.e. properties that are no properties at all).  In a sense,
<macrodef>'s current attributes are such uninterned symbols.

Incidentally I was reminded of (let) myself when I looked at the
<local> container.

> <let>
>   <local name="here" value="point"/>
>   <local name="ignore-depth value="0"/>
>   <local name="tag-info" value="context"/>
>   <echo>here is ${here}</echo>
> </let>
> 
> But this is not much different from: 
> <sequential>
>   <local name="here" value="point"/>
>   <local name="ignore-depth value="0"/>
>   <local name="tag-info" value="context"/>
>   <echo>here is ${here}</echo>
> </sequential>

Except that <sequential> has never provided any sort of scoping at
all, neither has <target>.  Making it explicit may help people to
understand the concept.

> This is done to support the following:
> <local name="x"/>
> <parallel>
>    <sequential>
>        <property name="x" value="1"/>
>        <echo>x is ${x}</echo>
>    </sequential>
>    <sequential>
>        <property name="x" value="2"/>
>        <echo>x is ${x}</echo>
>    </sequential>
>    <sequential>
>        <property name="x" value="3"/>
>        <echo>x is ${x}</echo>
>    </sequential>
> </parallel>

Feels wrong.  Each sequential should be/contain a <local> IMHO.  If
you want to have different local scopes withon the <sequential>s then
you have to create them.

Stefan

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