1Template::Alloy::Parse(U3s)er Contributed Perl DocumentatTieomnplate::Alloy::Parse(3)
2
6 Template::Alloy::Parse - Common parsing role for creating AST from
7 templates
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
21 syntax.
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
41 document. The remaining items are the variables necessary for
42 running 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 # $ast looks like [[undef, '+', 1, [[undef, '*', 2, 3], 0]], 0]
52 "parse_args"
54 Allow for the multitudinous ways that TT parses arguments. This
55 allows for positional as well as named arguments. Named arguments
56 can be separated with a "=" or "=>", and positional arguments
57 should be separated by " " or ",". This only returns an array of
58 parsed variables. To get the actual values, you must call
59 play_expr on each value.
60 "dump_parse_tree"
62 This method allows for returning a string of perl code representing
63 the AST of the parsed tree.
64 It is mainly used for testing.
66 "dump_parse_expr"
68 This method allows for returning a Data::Dumper dump of a parsed
69 variable. It is mainly used for testing.
70 "parse_*"
72 Methods by these names are used by parse_tree to parse the
73 template. These are the grammar. They are used by all of the
74 various template syntaxes Unless otherwise mentioned, these methods
75 are not exposed via the role.
76
78 Template::Alloy parses templates into an tree of operations (an AST or
79 abstract syntax tree). Even variable access is parsed into a tree.
80 This is done in a manner somewhat similar to the way that TT operates
81 except that nested variables such as foo.bar|baz contain the '.' or '|'
82 in between each name level. Operators are parsed and stored as part of
83 the variable (it may be more appropriate to say we are parsing a term
84 or an expression).
85 The following table shows a variable or expression and the
87 corresponding parsed tree (this is what the parse_expr method would
88 return).
89 one [ 'one', 0 ]
91 one() [ 'one', [] ]
92 one.two [ 'one', 0, '.', 'two', 0 ]
93 one|two [ 'one', 0, '|', 'two', 0 ]
94 one.$two [ 'one', 0, '.', ['two', 0 ], 0 ]
95 one(two) [ 'one', [ ['two', 0] ] ]
96 one.${two().three} [ 'one', 0, '.', ['two', [], '.', 'three', 0], 0]
97 2.34 2.34
98 "one" "one"
99 1 + 2 [ [ undef, '+', 1, 2 ], 0]
100 a + b [ [ undef, '+', ['a', 0], ['b', 0] ], 0 ]
101 "one"|length [ [ undef, '~', "one" ], 0, '|', 'length', 0 ]
102 "one $a two" [ [ undef, '~', 'one ', ['a', 0], ' two' ], 0 ]
103 [0, 1, 2] [ [ undef, '[]', 0, 1, 2 ], 0 ]
104 [0, 1, 2].size [ [ undef, '[]', 0, 1, 2 ], 0, '.', 'size', 0 ]
105 ['a', a, $a ] [ [ undef, '[]', 'a', ['a', 0], [['a', 0], 0] ], 0]
106 {a => 'b'} [ [ undef, '{}', 'a', 'b' ], 0 ]
107 {a => 'b'}.size [ [ undef, '{}', 'a', 'b' ], 0, '.', 'size', 0 ]
108 {$a => b} [ [ undef, '{}', ['a', 0], ['b', 0] ], 0 ]
109 a * (b + c) [ [ undef, '*', ['a', 0], [ [undef, '+', ['b', 0], ['c', 0]], 0 ]], 0 ]
110 (a + b) [ [ undef, '+', ['a', 0], ['b', 0] ]], 0 ]
111 (a + b) * c [ [ undef, '*', [ [undef, '+', ['a', 0], ['b', 0] ], 0 ], ['c', 0] ], 0 ]
112 a ? b : c [ [ undef, '?', ['a', 0], ['b', 0], ['c', 0] ], 0 ]
113 a || b || c [ [ undef, '||', ['a', 0], [ [undef, '||', ['b', 0], ['c', 0] ], 0 ] ], 0 ]
114 ! a [ [ undef, '!', ['a', 0] ], 0 ]
115 Some notes on the parsing.
117 Operators are parsed as part of the variable and become part of the variable tree.
119 Operators are stored in the variable tree using an operator identity array which
121 contains undef as the first value, the operator, and the operator arguments. This
122 allows for quickly descending the parsed variable tree and determining that the next
123 node is an operator.
124 Parenthesis () can be used at any point in an expression to disambiguate precedence.
126 "Variables" that appear to be literal strings or literal numbers
128 are returned as the literal (no operator tree).
129 The following perl can be typed at the command line to view the parsed
131 variable tree:
132 perl -e 'use Template::Alloy; print Template::Alloy->dump_parse_expr("foo.bar + 2")."\n"'
134 Also the following can be included in a template to view the output in
136 a template:
137 [% USE cet = Template::Alloy %]
139 [%~ cet.dump_parse_expr('foo.bar + 2').replace('\s+', ' ') %]
140
142 Paul Seamons <paul@seamons.com>
143
145 This module may be distributed under the same terms as Perl itself.
146perl v5.34.0 2022-01-21 Template::Alloy::Parse(3)