Provided by: libtemplate-alloy-perl_1.022-2_all bug

NAME

       Template::Alloy::Parse - Common parsing role for creating AST from templates

DESCRIPTION

       The Template::Alloy::Parse role is responsible 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.