1Template::Alloy::Parse(U3s)er Contributed Perl DocumentatTieomnplate::Alloy::Parse(3)
2
6 Template::Alloy::Parse - Common parsing role for creating AST from tem‐
7 plates
8
10 The Template::Alloy::Parse role is reponsible for storing the majority
11 of directive parsing code, as well as for delegating to the TT, HTE,
12 Tmpl, and Velocity roles for finding variables and directives.
13
15 parse_tree
16 Used by load_tree. This is the main grammar engine of the program.
17 It delegates to the syntax found in $self->{'SYNTAX'} (defaults to
18 'alloy') and calls the function found in the $SYNTAX hashref. The
19 majority of these syntaxes use methods found in the $DIRECTIVES
20 hashref to parse different DIRECTIVE types for each particular syn‐
21 tax.
22 A template that looked like the following:
24 Foo
26 [%- GET foo -%]
27 [%- GET bar -%]
28 Bar
29 would parse to the following AST:
31 [
33 'Foo',
34 ['GET', 6, 15, ['foo', 0]],
35 ['GET', 22, 31, ['bar', 0]],
36 'Bar',
37 ]
38 The "GET" words represent the directive used. The 6, 15 represent
40 the beginning and ending characters of the directive in the docu‐
41 ment. The remaining items are the variables necessary for running
42 the particular directive.
43 parse_expr
45 Used to parse a variable, an expression, a literal string, or a
46 number. It returns a parsed variable tree. Samples of parsed
47 variables can be found in the VARIABLE PARSE TREE section.
48 my $str = "1 + 2 * 3";
50 my $ast = $self->parse_expr(\$str);
51 # $ast looks like [[undef, '+', 1, [[undef, '*', 2, 3], 0]], 0]
52 "parse_args"
54 Allow for the multitudinous ways that TT parses arguments. This
55 allows for positional as well as named arguments. Named arguments
56 can be separated with a "=" or "=>", and positional arguments
57 should be separated by " " or ",". This only returns an array of
58 parsed variables. To get the actual values, you must call
59 play_expr on each value.
60 "dump_parse_tree"
62 This method allows for returning a string of perl code representing
63 the AST of the parsed tree.
64 It is mainly used for testing.
66 "dump_parse_expr"
68 This method allows for returning a Data::Dumper dump of a parsed
69 variable. It is mainly used for testing.
70 "parse_*"
72 Methods by these names are used by parse_tree to parse the tem‐
73 plate. These are the grammar. They are used by all of the various
74 template syntaxes Unless otherwise mentioned, these methods are not
75 exposed via the role.
76
78 Template::Alloy parses templates into an tree of operations (an AST or
79 abstract syntax tree). Even variable access is parsed into a tree.
80 This is done in a manner somewhat similar to the way that TT operates
81 except that nested variables such as foo.bar⎪baz contain the '.' or '⎪'
82 in between each name level. Operators are parsed and stored as part of
83 the variable (it may be more appropriate to say we are parsing a term
84 or an expression).
85 The following table shows a variable or expression and the correspond‐
87 ing parsed tree (this is what the parse_expr method would return).
88 one [ 'one', 0 ]
90 one() [ 'one', [] ]
91 one.two [ 'one', 0, '.', 'two', 0 ]
92 one⎪two [ 'one', 0, '⎪', 'two', 0 ]
93 one.$two [ 'one', 0, '.', ['two', 0 ], 0 ]
94 one(two) [ 'one', [ ['two', 0] ] ]
95 one.${two().three} [ 'one', 0, '.', ['two', [], '.', 'three', 0], 0]
96 2.34 2.34
97 "one" "one"
98 1 + 2 [ [ undef, '+', 1, 2 ], 0]
99 a + b [ [ undef, '+', ['a', 0], ['b', 0] ], 0 ]
100 "one"⎪length [ [ undef, '~', "one" ], 0, '⎪', 'length', 0 ]
101 "one $a two" [ [ undef, '~', 'one ', ['a', 0], ' two' ], 0 ]
102 [0, 1, 2] [ [ undef, '[]', 0, 1, 2 ], 0 ]
103 [0, 1, 2].size [ [ undef, '[]', 0, 1, 2 ], 0, '.', 'size', 0 ]
104 ['a', a, $a ] [ [ undef, '[]', 'a', ['a', 0], [['a', 0], 0] ], 0]
105 {a => 'b'} [ [ undef, '{}', 'a', 'b' ], 0 ]
106 {a => 'b'}.size [ [ undef, '{}', 'a', 'b' ], 0, '.', 'size', 0 ]
107 {$a => b} [ [ undef, '{}', ['a', 0], ['b', 0] ], 0 ]
108 a * (b + c) [ [ undef, '*', ['a', 0], [ [undef, '+', ['b', 0], ['c', 0]], 0 ]], 0 ]
109 (a + b) [ [ undef, '+', ['a', 0], ['b', 0] ]], 0 ]
110 (a + b) * c [ [ undef, '*', [ [undef, '+', ['a', 0], ['b', 0] ], 0 ], ['c', 0] ], 0 ]
111 a ? b : c [ [ undef, '?', ['a', 0], ['b', 0], ['c', 0] ], 0 ]
112 a ⎪⎪ b ⎪⎪ c [ [ undef, '⎪⎪', ['a', 0], [ [undef, '⎪⎪', ['b', 0], ['c', 0] ], 0 ] ], 0 ]
113 ! a [ [ undef, '!', ['a', 0] ], 0 ]
114 Some notes on the parsing.
116 Operators are parsed as part of the variable and become part of the variable tree.
118 Operators are stored in the variable tree using an operator identity array which
120 contains undef as the first value, the operator, and the operator arguments. This
121 allows for quickly descending the parsed variable tree and determining that the next
122 node is an operator.
123 Parenthesis () can be used at any point in an expression to disambiguate precedence.
125 "Variables" that appear to be literal strings or literal numbers
127 are returned as the literal (no operator tree).
128 The following perl can be typed at the command line to view the parsed
130 variable tree:
131 perl -e 'use Template::Alloy; print Template::Alloy->dump_parse_expr("foo.bar + 2")."\n"'
133 Also the following can be included in a template to view the output in
135 a template:
136 [% USE cet = Template::Alloy %]
138 [%~ cet.dump_parse_expr('foo.bar + 2').replace('\s+', ' ') %]
139
141 Paul Seamons <paul at seamons dot com>
142
144 This module may be distributed under the same terms as Perl itself.
145perl v5.8.8 2007-07-24 Template::Alloy::Parse(3)