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.
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.
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/.