Provided by: libtemplate-alloy-perl_1.020-1_all 
NAME
Template::Alloy::Parse - Common parsing role for creating AST from templates
DESCRIPTION
The Template::Alloy::Parse role is reponsible for storing the majority of directive
parsing code, as well as for delegating to the TT, HTE, Tmpl, and Velocity roles for
finding variables and directives.
ROLE METHODS
parse_tree
Used by load_tree. This is the main grammar engine of the program. It delegates to
the syntax found in $self->{'SYNTAX'} (defaults to 'alloy') and calls the function
found in the $SYNTAX hashref. The majority of these syntaxes use methods found in the
$DIRECTIVES hashref to parse different DIRECTIVE types for each particular syntax.
A template that looked like the following:
Foo
[%- GET foo -%]
[%- GET bar -%]
Bar
would parse to the following AST:
[
'Foo',
['GET', 6, 15, ['foo', 0]],
['GET', 22, 31, ['bar', 0]],
'Bar',
]
The "GET" words represent the directive used. The 6, 15 represent the beginning and
ending characters of the directive in the document. The remaining items are the
variables necessary for running the particular directive.
parse_expr
Used to parse a variable, an expression, a literal string, or a number. It returns a
parsed variable tree. Samples of parsed variables can be found in the VARIABLE PARSE
TREE section.
my $str = "1 + 2 * 3";
my $ast = $self->parse_expr(\$str);
# $ast looks like [[undef, '+', 1, [[undef, '*', 2, 3], 0]], 0]
"parse_args"
Allow for the multitudinous ways that TT parses arguments. This allows for positional
as well as named arguments. Named arguments can be separated with a "=" or "=>", and
positional arguments should be separated by " " or ",". This only returns an array of
parsed variables. To get the actual values, you must call play_expr on each value.
"dump_parse_tree"
This method allows for returning a string of perl code representing the AST of the
parsed tree.
It is mainly used for testing.
"dump_parse_expr"
This method allows for returning a Data::Dumper dump of a parsed variable. It is
mainly used for testing.
"parse_*"
Methods by these names are used by parse_tree to parse the template. These are the
grammar. They are used by all of the various template syntaxes Unless otherwise
mentioned, these methods are not exposed via the role.
VARIABLE PARSE TREE
Template::Alloy parses templates into an tree of operations (an AST or abstract syntax
tree). Even variable access is parsed into a tree. This is done in a manner somewhat
similar to the way that TT operates except that nested variables such as foo.bar|baz
contain the '.' or '|' in between each name level. Operators are parsed and stored as
part of the variable (it may be more appropriate to say we are parsing a term or an
expression).
The following table shows a variable or expression and the corresponding parsed tree (this
is what the parse_expr method would return).
one [ 'one', 0 ]
one() [ 'one', [] ]
one.two [ 'one', 0, '.', 'two', 0 ]
one|two [ 'one', 0, '|', 'two', 0 ]
one.$two [ 'one', 0, '.', ['two', 0 ], 0 ]
one(two) [ 'one', [ ['two', 0] ] ]
one.${two().three} [ 'one', 0, '.', ['two', [], '.', 'three', 0], 0]
2.34 2.34
"one" "one"
1 + 2 [ [ undef, '+', 1, 2 ], 0]
a + b [ [ undef, '+', ['a', 0], ['b', 0] ], 0 ]
"one"|length [ [ undef, '~', "one" ], 0, '|', 'length', 0 ]
"one $a two" [ [ undef, '~', 'one ', ['a', 0], ' two' ], 0 ]
[0, 1, 2] [ [ undef, '[]', 0, 1, 2 ], 0 ]
[0, 1, 2].size [ [ undef, '[]', 0, 1, 2 ], 0, '.', 'size', 0 ]
['a', a, $a ] [ [ undef, '[]', 'a', ['a', 0], [['a', 0], 0] ], 0]
{a => 'b'} [ [ undef, '{}', 'a', 'b' ], 0 ]
{a => 'b'}.size [ [ undef, '{}', 'a', 'b' ], 0, '.', 'size', 0 ]
{$a => b} [ [ undef, '{}', ['a', 0], ['b', 0] ], 0 ]
a * (b + c) [ [ undef, '*', ['a', 0], [ [undef, '+', ['b', 0], ['c', 0]], 0 ]], 0 ]
(a + b) [ [ undef, '+', ['a', 0], ['b', 0] ]], 0 ]
(a + b) * c [ [ undef, '*', [ [undef, '+', ['a', 0], ['b', 0] ], 0 ], ['c', 0] ], 0 ]
a ? b : c [ [ undef, '?', ['a', 0], ['b', 0], ['c', 0] ], 0 ]
a || b || c [ [ undef, '||', ['a', 0], [ [undef, '||', ['b', 0], ['c', 0] ], 0 ] ], 0 ]
! a [ [ undef, '!', ['a', 0] ], 0 ]
Some notes on the parsing.
Operators are parsed as part of the variable and become part of the variable tree.
Operators are stored in the variable tree using an operator identity array which
contains undef as the first value, the operator, and the operator arguments. This
allows for quickly descending the parsed variable tree and determining that the next
node is an operator.
Parenthesis () can be used at any point in an expression to disambiguate precedence.
"Variables" that appear to be literal strings or literal numbers
are returned as the literal (no operator tree).
The following perl can be typed at the command line to view the parsed variable tree:
perl -e 'use Template::Alloy; print Template::Alloy->dump_parse_expr("foo.bar + 2")."\n"'
Also the following can be included in a template to view the output in a template:
[% USE cet = Template::Alloy %]
[%~ cet.dump_parse_expr('foo.bar + 2').replace('\s+', ' ') %]
AUTHOR
Paul Seamons <paul@seamons.com>
LICENSE
This module may be distributed under the same terms as Perl itself.