Math in Template::Toolkit

talexb has asked for the wisdom of the Perl Monks concerning the following question:

I'm trying to do some relatively simple math in a template, and I appear to be running into an error. perhaps someone hear can suggest a solution.

 ...
 [%- IF top_menu.$base_name != '' -%]
 [%-   page_title = top_menu.$base_name -%]
 [%-   width = (100/(top_menu.$size)); -%]
 [%-   extra = (100-(width*(top_menu.$size))); -%]
 [%- ELSE -%]
 ...
[download]

This first sample compiles fine .. it has to do with setting up some nice spacing of menu items on a web page, nothing terribly exciting. But ..

 ...
 [%- IF top_menu.$base_name != '' -%]
 [%-   page_title = top_menu.$base_name -%]
 [%-   width = (100/(top_menu.$size)); -%]
 [%-   extra = ((100-(width*(top_menu.$size)))/2); -%]
 [%- ELSE -%]
 ...
[download]

gives me the error

file error - parse error - vb-template.tt2 line 31:
unexpected token (/2)
  [% extra = ((100-(width*(top_menu.$size)))/2); %]
[download]

I've looked through the man pages, asked on #perl, asked on #tt on irc.perl.org, and I'm now stuck.

Suggestions appreciated.

Alex / talexb / Toronto

"Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds

Comment on Math in Template::Toolkit Select or Download Code

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Re: Math in Template::Toolkit by kyle (Abbot) on Apr 30, 2007 at 03:43 UTC
What's in `top_menu`? I can imagine it's something like this: `$top_menu = { base_name => 'foo', size => 23 };` [download] And after your code executes, you expect `width = 3.03` and `extra = 0`. Yes? What your code actually does is something different. To get the `base_name` element in a `top_menu` hash in TT, it's `top_menu.base_name` (no dollar sign). If you say `top_menu.$base_name` in TT, it's like `$top_menu[$base_name]` in Perl. I could be wrong about this, however. I'd expect `top_menu.$size` to be zero if you haven't set `size` to anything in particular, so I'd expect `100/top_menu.$size` to bomb out as division by zero. Also, the error you're getting isn't really explained by what I'm talking about. Anyway, I think a Data::Dumper look into your variables might help. I also wonder if it would help to explicitly say `[%- SET extra = ((100-(width(top_menu.$size)))/2); -%]` [download] ...although I'm not sure why* that would help.	[reply] [d/l] [select]
Re: Math in Template::Toolkit by GrandFather (Saint) on Apr 30, 2007 at 02:48 UTC
Looks ok (correct bracket matching and such) so maybe you've hit a bug in the parser? Try variations like: `(100-(width(top_menu.$size)))/2 (50-(width(top_menu.$size)/2)) (100-(widthtop_menu.$size))/2 50-(widthtop_menu.$size)/2 50-width*top_menu.$size/2` [download] DWIM is Perl's answer to Gödel	[reply] [d/l]
Re^2: Math in Template::Toolkit by talexb (Chancellor) on Apr 30, 2007 at 02:54 UTC
Good idea, but .. `[% extra = width/2; %]; [% extra = (width/2); %] [% extra = ($width/2); %]` [download] all failed. :( Alex / talexb / Toronto "Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds	[reply] [d/l]
Re^3: Math in Template::Toolkit by mreece (Friar) on Apr 30, 2007 at 21:14 UTC
how about `width*.5` ? ;)	[reply] [d/l]
Re: Math in Template::Toolkit by Herkum (Parson) on Apr 30, 2007 at 12:03 UTC
I am willing to beat the error is further up the script than what you have shown us. The line you showed us is where the compiler decided were it thought the error was, not where the error actually is Consider moving your code out of the template and into a plugin. It would easier to read your template and I find it easier to debug Perl code rather than templates that do not compile.	[reply]
Re: Math in Template::Toolkit by FunkyMonk (Bishop) on Apr 30, 2007 at 20:40 UTC
Adding spaces around the divide works for me `zippy:~$ cat x [% width = 5 -%] [% extra = width / 2; -%] [%- extra %] zippy:~$ tpage x 2.5` [download]	[reply] [d/l]