Subject: Re: arrays really aren't - DN [1]
"Gerald W. Lester" <Gerald.Lester@cpu.com> - 14 May 1999 - comp.lang.tcl
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Phil wrote:
> Donal K. Fellows <fellowsd@cs.man.ac.uk> wrote:
> >In article <7hcfor$ani@gap.cco.caltech.edu>,
> >Phil <pehrens@ligo.caltech.edu> wrote:
> >> proc foo { bam } {
> >> array set ::bar {bim $bam}
> >> }
> >
> >You really meant:
> > proc foo {bam} {array set ::bar [list bim $bam]}
> >I forgive you though... :^)
>
> Okay, my generality was suffering a lapse, I concede!
>
> >> Amusingly, things like $::var and ::$var are equivalent.
> >
> >WRONG! They are most definitely not equivalent:
> >
> > % proc foo {bar} {puts "$::bar - ::$bar"}
> > % set bar 1; foo 0
> > 1 - ::0
>
> What about:
>
> set foo 12
> set ::$foo twelve
> set $foo --> twelve
> set $::foo TWELVE
> set $foo --> TWELVE
>
> Now it's even more disturbing, dont you think?
Not at all! The only thing disturbing is you forgetting *where*
substitutions happen at, i.e. in the parser. Lets look at what the set
command (at the C level, sees for its arguments) in each case:
set foo 12
Arg #1) foo
Arg #2) 12
Variable foo <= 12
set ::$foo twelve
Arg #1) ::12 (foo has already been substituted!)
Arg #2) twelve
Variable 12 <= twelve
set $foo --> twelve
Arg #1) 12 (foo has already been substituted!)
Returns the value of variable 12, i.e. twelve
set $::foo TWELVE
Arg #1) 12 (::foo, which is the same as foo, has already
been substituted!)
Arg #2) TWELVE
Variable 12 <= TWELVE
set $foo --> TWELVE
Arg #1) 12 (foo has already been substituted!)
Returns the value of variable 12, i.e. TWELVE
Tcl is very consistent, you just have to remember that it is interpretive
and the parser does the substitutions.
> The local variable "bar" in proc "foo" is not in the "" namespace
> in proc "foo". Where is it?
>
Here you appear be getting namespaces and scope (i.e. stack frames)
confused. They are two completely different things.
--
+--------------------------------+---------------------------------------+
| Gerald W. Lester | "The man who fights for his ideals is
|
| gerald_lester@bellsouth.net | the man who is alive." -- Cervantes
|
| Webmaster for http://www.mtolive-lcms.org
|
+--------------------------------+---------------------------------------+
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Phil wrote:
<blockquote TYPE=CITE>Donal K. Fellows <fellowsd@cs.man.ac.uk> wrote:
<br>>In article <7hcfor$ani@gap.cco.caltech.edu>,
<br>>Phil <pehrens@ligo.caltech.edu> wrote:
<br>>> proc foo { bam } {
<br>>> array set ::bar {bim $bam}
<br>>> }
<br>>
<br>>You really meant:
<br>> proc foo {bam} {array set ::bar [list bim $bam]}
<br>>I forgive you though... :^)
<p>Okay, my generality was suffering a lapse, I concede!
<p>>> Amusingly, things like $::var and ::$var are equivalent.
<br>>
<br>>WRONG! They are most definitely not equivalent:
<br>>
<br>> % proc foo {bar} {puts "$::bar - ::$bar"}
<br>> % set bar 1; foo 0
<br>> 1 - ::0
<p>What about:
<p>set foo 12
<br>set ::$foo twelve
<br>set $foo --> twelve
<br>set $::foo TWELVE
<br>set $foo --> TWELVE
<p>Now it's even more disturbing, dont you think?</blockquote>
Not at all! The only thing disturbing is you forgetting *where* substitutions
happen at, i.e. in the parser. Lets look at what the set command
(at the C level, sees for its arguments) in each case:
<p>set foo 12
<blockquote>Arg #1) foo
<br>Arg #2) 12
<p>Variable foo <= 12</blockquote>
set ::$foo twelve
<blockquote>Arg #1) ::12 (foo has already been substituted!)
<br>Arg #2) twelve
<p>Variable 12 <= twelve</blockquote>
set $foo --> twelve
<blockquote>Arg #1) 12 (foo has already been substituted!)
<p>Returns the value of variable 12, i.e. twelve</blockquote>
set $::foo TWELVE
<blockquote>Arg #1) 12 (::foo, which is the same as foo,
has already been substituted!)
<br>Arg #2) TWELVE
<p>Variable 12 <= TWELVE
<br> </blockquote>
set $foo --> TWELVE
<blockquote>Arg #1) 12 (foo has already been substituted!)
<p>Returns the value of variable 12, i.e. TWELVE</blockquote>
Tcl is very consistent, you just have to remember that it is interpretive
and the parser does the substitutions.
<br>
<blockquote TYPE=CITE>
<pre>The local variable "bar" in proc "foo" is not in the "" namespace
in proc "foo". Where is it?</pre>
</blockquote>
<p><br>Here you appear be getting namespaces and scope (i.e. stack frames)
confused. They are two completely different things.
<p><tt>--</tt>
<br><tt>+--------------------------------+---------------------------------------+</tt>
<br><tt>| Gerald W. Lester
| "The man who fights for his ideals is |</tt>
<br><tt>| gerald_lester@bellsouth.net | the man
who is alive." -- Cervantes |</tt>
<br><tt>|
Webmaster for <A HREF="http://www.mtolive-lcms.org">http://www.mtolive-lcms.org</A>
|</tt>
<br><tt>+--------------------------------+---------------------------------------+</tt>
<br> </html>
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Last modified
1999-09-27
1999-09-27
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