Provided by: libmarpa-r2-perl_2.086000~dfsg-6build2_amd64 
Name
Marpa::R2::Scanless::G - Scanless interface grammars
Synopsis
my $grammar = Marpa::R2::Scanless::G->new(
{
source => \(<<'END_OF_SOURCE'),
:default ::= action => do_first_arg
:start ::= Script
Script ::= Expression+ separator => comma action => do_script
comma ~ [,]
Expression ::=
Number
| '(' Expression ')' action => do_parens assoc => group
|| Expression '**' Expression action => do_pow assoc => right
|| Expression '*' Expression action => do_multiply
| Expression '/' Expression action => do_divide
|| Expression '+' Expression action => do_add
| Expression '-' Expression action => do_subtract
Number ~ [\d]+
:discard ~ whitespace
whitespace ~ [\s]+
# allow comments
:discard ~ <hash comment>
<hash comment> ~ <terminated hash comment> | <unterminated
final hash comment>
<terminated hash comment> ~ '#' <hash comment body> <vertical space char>
<unterminated final hash comment> ~ '#' <hash comment body>
<hash comment body> ~ <hash comment char>*
<vertical space char> ~ [\x{A}\x{B}\x{C}\x{D}\x{2028}\x{2029}]
<hash comment char> ~ [^\x{A}\x{B}\x{C}\x{D}\x{2028}\x{2029}]
END_OF_SOURCE
}
);
About this document
This page is the reference for the grammar objects of Marpa's Scanless interface.
Constructor
The "new()" method is the constructor for Scanless grammars. An example of its use is
above. The "new()" constructor accepts a hash of named arguments. The following named
arguments are allowed:
bless_package
Specifies the name of a Perl package. The package is used for blessing node values into a
Perl class, in conjunction with the "bless" adverb.
source
The value of the "source" named argument must be a reference to a string which contains a
description of the grammar. The string's format is a domain-specific language, described
in its own document.
trace_file_handle
The value is a file handle. Trace output and warning messages go to the trace file
handle. By default the trace file handle is "STDERR".
Discouraged named arguments
action_object
Use of this argument is discouraged in favor of the "semantics_package" named argument of
the SLIF recognizer. Like the "semantics_package" named argument, it sets the semantic
package. Unlike the "semantics_package" named argument, it is a fatal error if used
together with an explicit per-parse argument of the SLIF recognizer's "value()" method.
It is also a fatal error to try to use the "semantics_package" and "action_object"
arguments together.
default_action
Use of this argument is discouraged in favor of using the "action" adverb in a default
pseudo-rule. Specifies the "default_action" named argument that will be used for the G1
grammar. For details, see "default_action" in Marpa::R2::NAIF::Grammar.
Mutator
set()
$slg->set( { trace_file_handle => $trace_fh } );
This method allows the named arguments to be changed after an SLIF grammar is created.
Currently, the only argument that may be changed in "trace_file_handle".
Accessors
rule_expand()
my ($lhs_id, @rhs_ids) = $slg->rule_expand($rule_id);
$text .= "Rule #$rule_id: $lhs_id ::= " . (join q{ }, @rhs_ids) . "\n";
my ($lhs_id, @rhs_ids) = $slg->rule_expand($rule_id, 'L0');
$text .= "L0 Rule #$rule_id: $lhs_id ::= " . (join q{ }, @rhs_ids) . "\n";
"Expands" a rule ID into symbol ID's. An array of symbol ID's is returned. The ID of the
LHS symbol is the first element, and the remaining elements are the ID's of the RHS
symbols, in order. Returns an empty array if the rule does not exist.
The first argument is the ID of the rule to be "expanded". The second, optional, argument
is the name of a subgrammar. Currently there are L0 and G1 subgrammars. The default
subgrammar is G1.
rule_ids()
do_something($_) for $slg->rule_ids();
do_something($_) for $slg->rule_ids('L0');
Returns a list of the rule ID's as an array. Takes one, optional, argument: the name of a
subgrammar. Currently there are L0 and G1 subgrammars. The default subgrammar is G1.
rule_name()
push @rule_names, $slg->rule_name($_) for $slg->rule_ids();
Given a rule ID, returns the rule name. A rule name is as defined by the "name" adverb.
If no rule name was defined, the rule name is the name of the LHS symbol.
rule_show()
my $rule_description = $slg->rule_show($rule_id);
my $rule_description = $slg->rule_show($rule_id, 'L0');
For a rule ID, returns a string describing that rule in a form which is useful for tracing
and debugging, but subject to change. Returns a Perl undef if the rule does not exist.
The first argument is the ID of the rule to be displayed. The second, optional, argument
is the name of a subgrammar. Currently there are L0 and G1 subgrammars. The default
subgrammar is G1.
start_symbol_id()
my $start_id = $slg->start_symbol_id();
Returns the ID of the start symbol. Note that there is no method to return the ID of the
start rule, because there may be no unique start rule.
symbol_description()
my $description = $slg->symbol_description($symbol_id)
// '[No description]';
$text .= "symbol number: $symbol_id description $description\n";
my $description = $slg->symbol_description( $symbol_id, 'L0' )
// '[No description]';
$text .= "L0 symbol number: $symbol_id description $description\n";
Given a symbol ID, returns a description of the symbol. The description may not be
defined. Currently internal symbols tend to have descriptions, while symbols explicitly
specified by the user in the DSL are treated as self-explanatory. The description is
intended for humans to read, and is subject to change.
The first argument is the symbol ID. A second, optional, argument is the subgrammar.
Currently there are L0 and G1 subgrammars. The default subgrammar is G1. Returns a Perl
"undef" if the symbol does not exist, or if it has no description.
symbol_display_form()
my $display_form = $slg->symbol_display_form($symbol_id);
$text
.= "symbol number: $symbol_id name in display form: $display_form\n";
my $display_form = $slg->symbol_display_form( $symbol_id, 'L0' );
$text
.= "L0 symbol number: $symbol_id name in display form: $display_form\n";
Given a symbol ID, returns the "display form" of the symbol. This is the symbol in a form
thought most suitable for display in messages, etc. The display form is always defined.
The display form of a symbol is not useable as a name -- it is not necessarily unique, and
is subject to change.
The first argument is the symbol ID. A second, optional, argument is the subgrammar.
Currently there are L0 and G1 subgrammars. The default subgrammar is G1. Returns a Perl
"undef" if the symbol does not exist.
symbol_dsl_form()
my $dsl_form = $slg->symbol_dsl_form($symbol_id)
// '[No name in DSL form]';
$text .= "symbol number: $symbol_id DSL form: $dsl_form\n";
my $dsl_form = $slg->symbol_dsl_form( $symbol_id, 'L0' )
// '[No name in DSL form]';
$text .= "L0 symbol number: $symbol_id DSL form: $dsl_form\n";
Given a symbol ID, returns the "DSL form" of the symbol. This is the name of the symbol
in a form similar to the way it is specified by the user in the DSL. If the symbol has an
explicit name, the symbol's DSL form is the same as its explicit name. If the symbol does
not have an explicit name, the method may return a Perl "undef", or it may return a DSL
name invented by Marpa and intended to be suggestive. The DSL form of a symbol is not
intended for use as a symbol name -- it is not necessarily unique, is not always defined,
and it is subject to change.
The first argument is the symbol ID. A second, optional, argument is the subgrammar.
Currently there are L0 and G1 subgrammars. The default subgrammar is G1. Returns a Perl
"undef" if the symbol does not exist, or if it has no DSL form.
symbol_ids()
do_something($_) for $slg->symbol_ids();
do_something($_) for $slg->symbol_ids('L0');
Returns a list of the symbol ID's as an array. Takes one, optional, argument: the name of
a subgrammar. Currently there are L0 and G1 subgrammars. The default subgrammar is G1.
symbol_name()
my $name = $slg->symbol_name($symbol_id);
$text .= "symbol number: $symbol_id name: $name\n";
my $name = $slg->symbol_name( $symbol_id, 'L0' );
$text .= "L0 symbol number: $symbol_id name: $name\n";
Given a symbol ID, returns the name of the symbol. For every symbol ID, this method's
return value will be defined and will be unique to that symbol ID, so that it is suitable
for use as a symbol name. If a symbol has an explicit name, the return value will be the
symbol's explicit name. If there is no explicit name, it will be an internal name.
Internal names are subject to change.
The first argument is the symbol ID. A second, optional, argument is the subgrammar.
Currently there are L0 and G1 subgrammars. The default subgrammar is G1. Returns a Perl
"undef" if the symbol does not exist.
Trace methods
show_rules()
my $show_rules_output = $slg->show_rules();
$show_rules_output .= $slg->show_rules(3, 'L0');
The "show_rules()" method returns a descripton of the rules for a subgrammar, by default
G1. It is useful for understanding the rules as they appear in trace and debugging
outputs. To allow for improvements in Marpa::R2, the output of "show_rules()" is subject
to change.
The first optional argument can be a numeric verbosity level. The default verbosity is 1,
which is adequate for most purposes. A verbosity of 2 prints additional information
useful for those new to SLIF tracing and debugging. A verbosity of 3 prints additional
information for experts.
The second, optional, argument is the name of a subgrammar. Currently there are L0 and G1
subgrammars.
show_symbols()
$show_symbols_output .= $slg->show_symbols(3);
$show_symbols_output .= $slg->show_symbols(3, 'L0');
The "show_symbols()" method returns a descripton of the symbols for a subgrammar, by
default G1. It is useful for understanding the symbols as they appear in trace and
debugging outputs. To allow for improvements in Marpa::R2, the output of "show_symbols()"
is subject to change.
The first argument can be a numeric verbosity level. The default verbosity is 1, which is
adequate for most purposes. A verbosity of 2 prints additional information useful for
those new to SLIF tracing and debugging. A verbosity of 3 prints additional information
for experts.
The second, optional, argument is the name of a subgrammar. Currently there are L0 and G1
subgrammars.
Discouraged methods
Discouraged methods are those that continue to be supported, but whose use is discouraged
for one reason or another.
g0_rule()
my @g0_rule_ids = $slg->g0_rule_ids();
for my $g0_rule_id (@g0_rule_ids) {
$g0_rules_description .= "$g0_rule_id "
. ( join q{ }, map {"<$_>"} $slg->g0_rule($g0_rule_id) ) . "\n";
}
Please prefer "rule_expand()", together with "symbol_name()" or "symbol_display_form()".
Given a L0 rule ID as its argument, returns an array containing the names of the symbols
of that rule. The "g0_rule()" method returns a Perl false if no L0 rule with that rule ID
exists. If the L0 rule ID exists, "g0_rule()" returns a list of one or more symbol names.
The first symbol name will be that of the rule's LHS symbol. The rest of the list will be
the names of the rule's RHS symbols, in order.
g0_rule_ids()
my @g0_rule_ids = $slg->g0_rule_ids();
for my $g0_rule_id (@g0_rule_ids) {
$g0_rules_description .= "$g0_rule_id "
. ( join q{ }, map {"<$_>"} $slg->g0_rule($g0_rule_id) ) . "\n";
}
Please prefer "rule_expand()". Returns a list of the L0 rule ID's.
g1_rule_ids()
my @g1_rule_ids = $slg->g1_rule_ids();
for my $g1_rule_id (@g1_rule_ids) {
$g1_rules_description .= "$g1_rule_id "
. ( join q{ }, map {"<$_>"} $slg->rule($g1_rule_id) ) . "\n";
}
Please prefer "rule_expand()". Returns a list of the G1 rule ID's.
rule()
my @g1_rule_ids = $slg->g1_rule_ids();
for my $g1_rule_id (@g1_rule_ids) {
$g1_rules_description .= "$g1_rule_id "
. ( join q{ }, map {"<$_>"} $slg->rule($g1_rule_id) ) . "\n";
}
Please prefer "rule_expand()", together with "symbol_name()" or "symbol_display_form()".
Given a G1 rule ID as its argument, returns an array containing the names of the symbols
of that rule. The "rule()" method returns a Perl false if no G1 rule with that rule ID
exists. If the rule ID exists, "rule()" returns a list of one or more symbol names. The
first symbol name will be that of the rule's LHS symbol. The rest of the list will be the
names of the rule's RHS symbols, in order. The SLIF's "rule()" method is useful in
combination with the SLIF's of the progress method, whose output identifies rules by rule
ID.
Copyright and License
Copyright 2014 Jeffrey Kegler
This file is part of Marpa::R2. Marpa::R2 is free software: you can
redistribute it and/or modify it under the terms of the GNU Lesser
General Public License as published by the Free Software Foundation,
either version 3 of the License, or (at your option) any later version.
Marpa::R2 is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser
General Public License along with Marpa::R2. If not, see
http://www.gnu.org/licenses/.