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.\" ========================================================================
.\"
.IX Title "Marpa::R2::Scanless::G 3pm"
.TH Marpa::R2::Scanless::G 3pm 2024-03-06 "perl v5.38.2" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH Name
.IX Header "Name"
Marpa::R2::Scanless::G \- Scanless interface grammars
.SH Synopsis
.IX Header "Synopsis"
.Vb 10
\&    my $grammar = Marpa::R2::Scanless::G\->new(
\&        {   
\&            source          => \e(<<\*(AqEND_OF_SOURCE\*(Aq),
\&    :default ::= action => do_first_arg
\&    :start ::= Script
\&    Script ::= Expression+ separator => comma action => do_script
\&    comma ~ [,]
\&    Expression ::=
\&        Number
\&        | \*(Aq(\*(Aq Expression \*(Aq)\*(Aq action => do_parens assoc => group
\&       || Expression \*(Aq**\*(Aq Expression action => do_pow assoc => right
\&       || Expression \*(Aq*\*(Aq Expression action => do_multiply
\&        | Expression \*(Aq/\*(Aq Expression action => do_divide
\&       || Expression \*(Aq+\*(Aq Expression action => do_add
\&        | Expression \*(Aq\-\*(Aq Expression action => do_subtract
\&    Number ~ [\ed]+
\&
\&    :discard ~ whitespace
\&    whitespace ~ [\es]+
\&    # allow comments
\&    :discard ~ <hash comment>
\&    <hash comment> ~ <terminated hash comment> | <unterminated
\&       final hash comment>
\&    <terminated hash comment> ~ \*(Aq#\*(Aq <hash comment body> <vertical space char>
\&    <unterminated final hash comment> ~ \*(Aq#\*(Aq <hash comment body>
\&    <hash comment body> ~ <hash comment char>*
\&    <vertical space char> ~ [\ex{A}\ex{B}\ex{C}\ex{D}\ex{2028}\ex{2029}]
\&    <hash comment char> ~ [^\ex{A}\ex{B}\ex{C}\ex{D}\ex{2028}\ex{2029}]
\&    END_OF_SOURCE
\&        }
\&    );
.Ve
.SH "About this document"
.IX Header "About this document"
This page is the reference for the grammar objects
of Marpa's Scanless interface.
.SH Constructor
.IX Header "Constructor"
The \f(CWnew()\fR method is the constructor for Scanless grammars.
An example of its use is above.
The \f(CWnew()\fR constructor accepts a hash of named arguments.
The following named arguments are allowed:
.SS bless_package
.IX Subsection "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
\&\f(CW\*(C`bless\*(C'\fR adverb.
.SS source
.IX Subsection "source"
The value of the \f(CW\*(C`source\*(C'\fR 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.
.SS trace_file_handle
.IX Subsection "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 \f(CW\*(C`STDERR\*(C'\fR.
.SS "Discouraged named arguments"
.IX Subsection "Discouraged named arguments"
\fIaction_object\fR
.IX Subsection "action_object"
.PP
Use of this argument is discouraged
in favor of the \f(CW\*(C`semantics_package\*(C'\fR named argument of the SLIF
recognizer.
Like the \f(CW\*(C`semantics_package\*(C'\fR named argument, it sets the semantic
package.
Unlike the \f(CW\*(C`semantics_package\*(C'\fR named argument, it is a fatal error if used
together with an explicit per-parse argument of the SLIF recognizer's \f(CWvalue()\fR method.
It is also a fatal error to try to use the \f(CW\*(C`semantics_package\*(C'\fR
and \f(CW\*(C`action_object\*(C'\fR arguments together.
.PP
\fIdefault_action\fR
.IX Subsection "default_action"
.PP
Use of this argument is discouraged in favor of using the
\&\f(CW\*(C`action\*(C'\fR adverb
in a
default pseudo-rule.
Specifies the \f(CW\*(C`default_action\*(C'\fR named argument that
will be used for the G1 grammar.
For details, see "default_action" in Marpa::R2::NAIF::Grammar.
.SH Mutator
.IX Header "Mutator"
.SS \fBset()\fP
.IX Subsection "set()"
.Vb 1
\&    $slg\->set( { trace_file_handle => $trace_fh } );
.Ve
.PP
This method allows the named arguments to be changed after an SLIF
grammar is created.
Currently, the only argument that may be changed in \f(CW\*(C`trace_file_handle\*(C'\fR.
.SH Accessors
.IX Header "Accessors"
.SS \fBrule_expand()\fP
.IX Subsection "rule_expand()"
.Vb 2
\&    my ($lhs_id, @rhs_ids) = $slg\->rule_expand($rule_id);
\&    $text .= "Rule #$rule_id: $lhs_id ::= " . (join q{ }, @rhs_ids) . "\en";
.Ve
.PP
.Vb 2
\&    my ($lhs_id, @rhs_ids) = $slg\->rule_expand($rule_id, \*(AqL0\*(Aq);
\&    $text .= "L0 Rule #$rule_id: $lhs_id ::= " . (join q{ }, @rhs_ids) . "\en";
.Ve
.PP
"Expands" a rule ID into symbol ID's.
An array of symbol ID's is returned.
The ID of the LHS symbol is the first element,
and the remaining elements are the ID's of the RHS symbols,
in order.
Returns an empty array if the rule does not exist.
.PP
The first argument is the ID of the rule to be "expanded".
The second, optional, argument is the name of a subgrammar.
Currently there are L0 and G1 subgrammars.
The default subgrammar is G1.
.SS \fBrule_ids()\fP
.IX Subsection "rule_ids()"
.Vb 1
\&    do_something($_) for $slg\->rule_ids();
.Ve
.PP
.Vb 1
\&    do_something($_) for $slg\->rule_ids(\*(AqL0\*(Aq);
.Ve
.PP
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.
.SS \fBrule_name()\fP
.IX Subsection "rule_name()"
.Vb 1
\&    push @rule_names, $slg\->rule_name($_) for $slg\->rule_ids();
.Ve
.PP
Given a rule ID, returns the rule name.
A rule name is as defined by
the \f(CW\*(C`name\*(C'\fR adverb.
If no rule name was defined, the rule name is the name of
the LHS symbol.
.SS \fBrule_show()\fP
.IX Subsection "rule_show()"
.Vb 1
\&    my $rule_description = $slg\->rule_show($rule_id);
.Ve
.PP
.Vb 1
\&    my $rule_description = $slg\->rule_show($rule_id, \*(AqL0\*(Aq);
.Ve
.PP
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.
.PP
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.
.SS \fBstart_symbol_id()\fP
.IX Subsection "start_symbol_id()"
.Vb 1
\&    my $start_id = $slg\->start_symbol_id();
.Ve
.PP
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.
.SS \fBsymbol_description()\fP
.IX Subsection "symbol_description()"
.Vb 3
\&    my $description = $slg\->symbol_description($symbol_id)
\&        // \*(Aq[No description]\*(Aq;
\&    $text .= "symbol number: $symbol_id  description $description\en";
.Ve
.PP
.Vb 3
\&    my $description = $slg\->symbol_description( $symbol_id, \*(AqL0\*(Aq )
\&        // \*(Aq[No description]\*(Aq;
\&    $text .= "L0 symbol number: $symbol_id  description $description\en";
.Ve
.PP
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.
.PP
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 \f(CW\*(C`undef\*(C'\fR if the symbol does not exist,
or if it has no description.
.SS \fBsymbol_display_form()\fP
.IX Subsection "symbol_display_form()"
.Vb 3
\&    my $display_form = $slg\->symbol_display_form($symbol_id);
\&    $text
\&        .= "symbol number: $symbol_id  name in display form: $display_form\en";
.Ve
.PP
.Vb 3
\&    my $display_form = $slg\->symbol_display_form( $symbol_id, \*(AqL0\*(Aq );
\&    $text
\&        .= "L0 symbol number: $symbol_id  name in display form: $display_form\en";
.Ve
.PP
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.
.PP
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 \f(CW\*(C`undef\*(C'\fR if the symbol does not exist.
.SS \fBsymbol_dsl_form()\fP
.IX Subsection "symbol_dsl_form()"
.Vb 3
\&    my $dsl_form = $slg\->symbol_dsl_form($symbol_id)
\&        // \*(Aq[No name in DSL form]\*(Aq;
\&    $text .= "symbol number: $symbol_id  DSL form: $dsl_form\en";
.Ve
.PP
.Vb 3
\&    my $dsl_form = $slg\->symbol_dsl_form( $symbol_id, \*(AqL0\*(Aq )
\&        // \*(Aq[No name in DSL form]\*(Aq;
\&    $text .= "L0 symbol number: $symbol_id  DSL form: $dsl_form\en";
.Ve
.PP
Given a symbol ID, returns the "DSL form" of the symbol.
This is the name of the symbol in a form similar
to the way it is specified by the user in the DSL.
If the symbol has an explicit name,
the symbol's DSL form is the same as its explicit name.
If the symbol does not have an explicit name,
the method may return a Perl \f(CW\*(C`undef\*(C'\fR,
or it may return a DSL name invented by Marpa
and intended to be suggestive.
The DSL form of a symbol is not intended for use as a symbol name
\&\-\- it is not necessarily unique,
is not always defined,
and it is subject to change.
.PP
The first argument is the symbol ID.
A second, optional, argument is the subgrammar.
Currently there are L0 and G1 subgrammars.
The default subgrammar is G1.
Returns a Perl \f(CW\*(C`undef\*(C'\fR if the symbol does not exist,
or if it has no DSL form.
.SS \fBsymbol_ids()\fP
.IX Subsection "symbol_ids()"
.Vb 1
\&    do_something($_) for $slg\->symbol_ids();
.Ve
.PP
.Vb 1
\&    do_something($_) for $slg\->symbol_ids(\*(AqL0\*(Aq);
.Ve
.PP
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.
.SS \fBsymbol_name()\fP
.IX Subsection "symbol_name()"
.Vb 2
\&    my $name = $slg\->symbol_name($symbol_id);
\&    $text .= "symbol number: $symbol_id  name: $name\en";
.Ve
.PP
.Vb 2
\&    my $name = $slg\->symbol_name( $symbol_id, \*(AqL0\*(Aq );
\&    $text .= "L0 symbol number: $symbol_id  name: $name\en";
.Ve
.PP
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.
.PP
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 \f(CW\*(C`undef\*(C'\fR if the symbol does not exist.
.SH "Trace methods"
.IX Header "Trace methods"
.SS \fBshow_rules()\fP
.IX Subsection "show_rules()"
.Vb 1
\&    my $show_rules_output = $slg\->show_rules();
.Ve
.PP
.Vb 1
\&    $show_rules_output .= $slg\->show_rules(3, \*(AqL0\*(Aq);
.Ve
.PP
The \f(CWshow_rules()\fR 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 \f(CWshow_rules()\fR is subject to change.
.PP
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.
.PP
The second, optional, argument is the name of a subgrammar.
Currently there are L0 and G1 subgrammars.
.SS \fBshow_symbols()\fP
.IX Subsection "show_symbols()"
.Vb 1
\&    $show_symbols_output .= $slg\->show_symbols(3);
.Ve
.PP
.Vb 1
\&    $show_symbols_output .= $slg\->show_symbols(3, \*(AqL0\*(Aq);
.Ve
.PP
The \f(CWshow_symbols()\fR 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 \f(CWshow_symbols()\fR is subject to change.
.PP
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.
.PP
The second, optional, argument is the name of a subgrammar.
Currently there are L0 and G1 subgrammars.
.SH "Discouraged methods"
.IX Header "Discouraged methods"
Discouraged methods are those that
continue to be supported, but whose use is discouraged for one
reason or another.
.SS \fBg0_rule()\fP
.IX Subsection "g0_rule()"
.Vb 5
\&    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) ) . "\en";
\&    }
.Ve
.PP
Please prefer "\fBrule_expand()\fR", together with
"\fBsymbol_name()\fR" or
"\fBsymbol_display_form()\fR".
Given a L0 rule ID as its argument,
returns an array containing the
names of the symbols of that rule.
The \f(CWg0_rule()\fR method
returns a Perl false if no L0 rule with that rule ID exists.
If the L0 rule ID exists,
\&\f(CWg0_rule()\fR 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.
.SS \fBg0_rule_ids()\fP
.IX Subsection "g0_rule_ids()"
.Vb 5
\&    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) ) . "\en";
\&    }
.Ve
.PP
Please prefer "\fBrule_expand()\fR".
Returns a list of the L0 rule ID's.
.SS \fBg1_rule_ids()\fP
.IX Subsection "g1_rule_ids()"
.Vb 5
\&    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) ) . "\en";
\&    }
.Ve
.PP
Please prefer "\fBrule_expand()\fR".
Returns a list of the G1 rule ID's.
.SS \fBrule()\fP
.IX Subsection "rule()"
.Vb 5
\&    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) ) . "\en";
\&    }
.Ve
.PP
Please prefer "\fBrule_expand()\fR", together with
"\fBsymbol_name()\fR" or
"\fBsymbol_display_form()\fR".
Given a G1 rule ID as its argument,
returns an array containing the
names of the symbols of that rule.
The \f(CWrule()\fR method
returns a Perl false if no G1 rule with that rule ID exists.
If the rule ID exists,
\&\f(CWrule()\fR 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 \f(CWrule()\fR method is useful in
combination with
the SLIF's
of the progress method,
whose output identifies rules by rule ID.
.SH "Copyright and License"
.IX Header "Copyright and License"
.Vb 5
\&  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/.
.Ve