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# TODO list for the Template Toolkit version 2.20, containing
# known bugs, limitations, planned enhancements, long term visions
# and a few whacky ideas. Development on TT2 has effectively
# ceased for everything but bug fixes. All new features and general
# enhancements are being saved for TT3.
# Andy Wardley <>
# Miscellaneous
* The 'eval' filter leaks memory, as reported by Colin Johnson. The
filter subroutine created contains a reference to the context and then
gets cached in the FILTER_CACHE item of the context. Hey presto -
circular references. The reset() method should probably clear the
FILTER_CACHE. Also need to check the plugins cache for similar
problems. UPDATE: this may now have been fixed.
* The handling of the DELIMITER parameter could be improved. At the
moments it's hardcoded and hacked to Do The Right Thing for Win32
but I'd prefer it to Do The Good Thing.
* If you use 'ttree' with a COMPILE_EXT or COMPILE_DIR option then
templates in the 'lib' directories will be compiled, but those in
the src directories will not. This is because ttree does a chdir()
to the src directory and processes files as './myfile'. TT doesn't
compile RELATIVE files by default.
* No recursion checking is performed for BLOCKs, only
Template::Document instances. This is probably the way it will stay
(unless anyone shouts loudly enough) but it should be documented
anyway. STOP PRESS: I had an idea that bare BLOCK subs should be
blessed into Template::Document class to allow $template->process()
to be called regardless. Template::Document methods would need to
test $self for CODE/HASH and Do The Right Thing. This would then
allow recursion testing for BLOCKs as well as Template::Document
* It would be nice if there was an option so that the files generated
under the COMPILE_DIR are relative to the INCLUDE_PATH and not absolute.
This could cause potential conflicts (e.g. if INCLUDE_PATH changes
between sessions and the same files in different INCLUDE_PATH dirs
maps to the samed compiled version) but is convenient for those times
when you know that's not going to be a problem.
* Craig Barratt notes, in fixing the problem with NEXT not working
inside SWITCH (see Changes v2.04):
By the way, I came across another arcane bug:
is legal syntax but is an infinite loop, since $_[0]->{ INFOR } in
Parser.yp is not set when the NEXT is parsed, so it generates a
plain "next;" rather than calling $factor->next(). I don't see an
easy, clean fix.
# Documentation
* Extend the FAQ.
# Directives
* A 'FOR', like 'FOREACH' but without using an iterator. You wouldn't get
the 'loop' reference to test 'first', 'last', etc., against, but it would
be faster for those cases when you didn't need it. This will likely
be implemented as a facility feature (see later).
* PRINT should be defined as a new directive, doing what the print()
method of Template::View currently does (the Right Thing).
[% PRINT node %] === [% tt.view.print(node) %]
NOTE TO SELF: this is a Very Good Idea [tm]. PRINT becomes the way to
display a data structure (e.g. hash, list, XML element, MyThingy, database
record, etc.) in an "intelligent" fashion. Implemented underneath via
the current default VIEW.
* ARGS. There may be a requirement for reusable template components
to define what variables they plan to use. This would allow some
optimisation and also possibly help to avoid global variable clashes.
Would also be a useful "comment" directive for human readers and maybe
also help in debugging (WARNING: expected 'title' argument).
[% ARGS title # no default
bgcol='#ffffff' # default value
# Parser
* Lists don't accept arbitrary expressions as elements, although
function arguments now do. So you can do this: [% foo(bar + 1) %],
but you can't do this: [% foo = [bar + 1] %]. This has been fixed in
the v3 parser.
* The parser isn't as intelligent as it could be about blocks of template
code commented out en masse. The pre-scanner find the first terminating
END_TAG after an opening tag, regardless of it being on a
commented line or not.
# [% INCLUDE blah %] <- directive ends here
# foo <- this gets printed
* Craig Barratt reports the following:
I looked at Parse.yp to see how hard it would be to push FILTER
evaluation down into the expr rule, so that you could put filters
inside expressions (eg: using repeat() just like &quot;x&quot; in
perl). More about that later.
In browsing through Parser.yp I noticed several issues:
- The operator precedence is very different to perl, C etc.
For example, these expressions evaluate differently in
TT2 versus perl, C etc:
+ "1 || 0 && 0" evaluates to 0 in TT2 and 1 in perl or C.
TT2 parses it as (1||0) && 0; in perl and C && is higher
precedence than ||.
+ "1 + !0 + 1" evaluates to 1 in TT2 and 3 in perl or C.
TT2 parses it as 1 + !(0 + 1); in perl and C ! is higher
precedence than +.
+ Many other expressions parse incorrectly, but the effect
is benign since most rules return flat text that perl
correctly re-parses. Eg, 2 * 3 + 4 is incorrectly parsed
as (2 * (3 + 4)), but happily just the string "2 * 3 + 4"
is compiled by perl, which correctly evaluates it as
(2 * 3) + 4.
- There is no unary minus and the NUMBER token is signed. So you can
write "x = -2;" but not "x = -y;". Moreover, "x = 1 -1;" is a syntax
error (since "1 -1" returns just two tokens NUMBER, NUMBER). (As a
workaround you can rewrite these as "x = 0-y;" and "x = 1 - 1".)
- You cannot have expressions in lists ([..]) and function arguments.
I have modified the (to make NUMBER unsigned) and modified and Parser.yp to fix most of these issues (improved
operator precedence, unary minus and plus), and also to allow
expressions in a few more places (eg: range). But the last item
has me stuck.
The parse rules for lists and function arguments make COMMA optional,
so you can equivalently write [1 2 3 4] or [1,,,,,2 3 4] or [1,2,3,4].
This makes it very difficult to make each term an expression, because
the resulting grammar has many ambiguities. For example, is [1 -1]
two elements [1, -1] or a single element [0]? One partial solution is
to move the bracketed expression rule '(' expr ')' to the term rule,
allowing expressions to be included via parens. But there are also
ambiguities, eg: does [foo (1+1)] have 2 elements or is it a function
call to foo?
Without allowing expressions in lists or function arguments, the unary
minus change I've made means that the NUMBER token is unsigned, so with
my changes you cannot write [-1, 2, 3]. Not a good thing.
One solution is to change the grammar so that COMMAs are required in
lists and arguments, but that would break several test cases and
probably break lots of old templates. But this might be the only
way to produce a grammar that is a lot more similar to perl.
Another solution is to ignore these issues altogether and use temporary
variables to precompute expressions that you need in lists or function
arguments, or use explicit lvalue assignments, eg:
foo(x + 2); becomes temp = x + 2;
List = [x+1,x+2,x+4]; becomes List = [];
List.0 = x+1;
List.1 = x+2;
List.2 = x+4;
Both of these look ugly to me.
Back to the FILTER issues. Ultimately I'd like to be able to embed filters
as low precedence operators in expressions, and write:
List = [
"foo" | repeat(10),
"bar" | repeat(10)
but I doubt there is a non-ambiguous upward compatible grammar that
supports this.
# Plugins
* We need a way to easily enable/disable certain plugins. This should
be addressed by facility provision. Probably something for v3.
* The Template::Plugin DBI iterator first/last() methods don't behave
the same as list first/last(). Randal also reports that get_all()
doesn't work as it should - may be a conflict in code/docs? Again,
this is a problem to solve in TT3.
* PLUGINS could accept a reference to an object which is used as a
singleton factory for a plugin. (NOTE: 2.01 includes PLUGIN_FACTORY
to implement this, but currently undocumented because it's likely to
* A more general solution for XML (e.g. DOM, XPath, etc) would be for
TT to support a PerlSAX handler which generates the appropriate
callbacks to the view. This should make it possible to easily
display XML content from XML::DOM, XML::XPath, or any other SAX
compliant source.
Something like this:
# define a view
[% VIEW my_view
prefix="my/xml/dom/path/" ;
# get some XML
[% USE dom = XML.DOM %]
[% doc = dom.parser(my.files.xmldata) %]
# ask the view to print the data
[% my_view.print(doc) %]
The view print() method will call the relevant 2SAX method on the
XML node, passing a SAX2TTView handler to make the relevant calls
back to the view to display parts of the XML data model as SAX events
are received.
# Views
The current implementation is there to get me (and anybody else who's
interested) using it and trying to identify the problems, requirements
and general issues involved. I've got a better idea now about what a
VIEW should be in notional terms, but I'm still not quite sure about
the syntax and API.
General thoughts:
* A view defines a set of templates. Things like prefix, suffix,
default, etc., can be specified to customise template selection.
In this sense, it is like a custom provider of those templates.
It implements the template() method to fetch a template according
to those rules.
* It is also a custom processor of those templates. It implements the
process() method. In this sense, it is like a custom context.
* It also implements dispatch logic to apply the right template to the
right kind of data. It does this via the print() method. It may
have all kinds of custom dispatch logic.
* A view takes responsiblity for things template related as opposed
to anything data related (stash) or application logic related
(plugins, runtime code, etc). It is the user interface facility
within the engine.