Template::Alloy::ParseUser Contributed Perl DocumentaTemplate::Alloy::Parse(3)NAMETemplate::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 at seamons dot com>
LICENSE
This module may be distributed under the same terms as Perl itself.
perl v5.14.1 2011-01-26 Template::Alloy::Parse(3)
