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.\" ========================================================================
.\"
.IX Title "TAP::Parser::Grammar 3perl"
.TH TAP::Parser::Grammar 3perl "2021-09-24" "perl v5.32.1" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
TAP::Parser::Grammar \- A grammar for the Test Anything Protocol.
.SH "VERSION"
.IX Header "VERSION"
Version 3.42
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 6
\&  use TAP::Parser::Grammar;
\&  my $grammar = $self\->make_grammar({
\&    iterator => $tap_parser_iterator,
\&    parser   => $tap_parser,
\&    version  => 12,
\&  });
\&
\&  my $result = $grammar\->tokenize;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`TAP::Parser::Grammar\*(C'\fR tokenizes lines from a TAP::Parser::Iterator and
constructs TAP::Parser::Result subclasses to represent the tokens.
.PP
Do not attempt to use this class directly.  It won't make sense.  It's mainly
here to ensure that we will be able to have pluggable grammars when \s-1TAP\s0 is
expanded at some future date (plus, this stuff was really cluttering the
parser).
.SH "METHODS"
.IX Header "METHODS"
.SS "Class Methods"
.IX Subsection "Class Methods"
\fI\f(CI\*(C`new\*(C'\fI\fR
.IX Subsection "new"
.PP
.Vb 5
\&  my $grammar = TAP::Parser::Grammar\->new({
\&      iterator => $iterator,
\&      parser   => $parser,
\&      version  => $version,
\&  });
.Ve
.PP
Returns TAP::Parser grammar object that will parse the \s-1TAP\s0 stream from the
specified iterator.  Both \f(CW\*(C`iterator\*(C'\fR and \f(CW\*(C`parser\*(C'\fR are required arguments.
If \f(CW\*(C`version\*(C'\fR is not set it defaults to \f(CW12\fR (see \*(L"set_version\*(R" for more
details).
.SS "Instance Methods"
.IX Subsection "Instance Methods"
\fI\f(CI\*(C`set_version\*(C'\fI\fR
.IX Subsection "set_version"
.PP
.Vb 1
\&  $grammar\->set_version(13);
.Ve
.PP
Tell the grammar which \s-1TAP\s0 syntax version to support. The lowest
supported version is 12. Although '\s-1TAP\s0 version' isn't valid version 12
syntax it is accepted so that higher version numbers may be parsed.
.PP
\fI\f(CI\*(C`tokenize\*(C'\fI\fR
.IX Subsection "tokenize"
.PP
.Vb 1
\&  my $token = $grammar\->tokenize;
.Ve
.PP
This method will return a TAP::Parser::Result object representing the
current line of \s-1TAP.\s0
.PP
\fI\f(CI\*(C`token_types\*(C'\fI\fR
.IX Subsection "token_types"
.PP
.Vb 1
\&  my @types = $grammar\->token_types;
.Ve
.PP
Returns the different types of tokens which this grammar can parse.
.PP
\fI\f(CI\*(C`syntax_for\*(C'\fI\fR
.IX Subsection "syntax_for"
.PP
.Vb 1
\&  my $syntax = $grammar\->syntax_for($token_type);
.Ve
.PP
Returns a pre-compiled regular expression which will match a chunk of \s-1TAP\s0
corresponding to the token type.  For example (not that you should really pay
attention to this, \f(CW\*(C`$grammar\->syntax_for(\*(Aqcomment\*(Aq)\*(C'\fR will return
\&\f(CW\*(C`qr/^#(.*)/\*(C'\fR.
.PP
\fI\f(CI\*(C`handler_for\*(C'\fI\fR
.IX Subsection "handler_for"
.PP
.Vb 1
\&  my $handler = $grammar\->handler_for($token_type);
.Ve
.PP
Returns a code reference which, when passed an appropriate line of \s-1TAP,\s0
returns the lexed token corresponding to that line.  As a result, the basic
\&\s-1TAP\s0 parsing loop looks similar to the following:
.PP
.Vb 10
\& my @tokens;
\& my $grammar = TAP::Grammar\->new;
\& LINE: while ( defined( my $line = $parser\->_next_chunk_of_tap ) ) {
\&     for my $type ( $grammar\->token_types ) {
\&         my $syntax  = $grammar\->syntax_for($type);
\&         if ( $line =~ $syntax ) {
\&             my $handler = $grammar\->handler_for($type);
\&             push @tokens => $grammar\->$handler($line);
\&             next LINE;
\&         }
\&     }
\&     push @tokens => $grammar\->_make_unknown_token($line);
\& }
.Ve
.SH "TAP GRAMMAR"
.IX Header "TAP GRAMMAR"
\&\fB\s-1NOTE:\s0\fR  This grammar is slightly out of date.  There's still some discussion
about it and a new one will be provided when we have things better defined.
.PP
The TAP::Parser does not use a formal grammar because \s-1TAP\s0 is essentially a
stream-based protocol.  In fact, it's quite legal to have an infinite stream.
For the same reason that we don't apply regexes to streams, we're not using a
formal grammar here.  Instead, we parse the \s-1TAP\s0 in lines.
.PP
For purposes for forward compatibility, any result which does not match the
following grammar is currently referred to as
TAP::Parser::Result::Unknown.  It is \fInot\fR a parse error.
.PP
A formal grammar would look similar to the following:
.PP
.Vb 4
\& (*
\&     For the time being, I\*(Aqm cheating on the EBNF by allowing
\&     certain terms to be defined by POSIX character classes by
\&     using the following syntax:
\&
\&       digit ::= [:digit:]
\&
\&     As far as I am aware, that\*(Aqs not valid EBNF.  Sue me.  I
\&     didn\*(Aqt know how to write "char" otherwise (Unicode issues).
\&     Suggestions welcome.
\& *)
\&
\& tap            ::= version? { comment | unknown } leading_plan lines
\&                    |
\&                    lines trailing_plan {comment}
\&
\& version        ::= \*(AqTAP version \*(Aq positiveInteger {positiveInteger} "\en"
\&
\& leading_plan   ::= plan skip_directive? "\en"
\&
\& trailing_plan  ::= plan "\en"
\&
\& plan           ::= \*(Aq1..\*(Aq nonNegativeInteger
\&
\& lines          ::= line {line}
\&
\& line           ::= (comment | test | unknown | bailout ) "\en"
\&
\& test           ::= status positiveInteger? description? directive?
\&
\& status         ::= \*(Aqnot \*(Aq? \*(Aqok \*(Aq
\&
\& description    ::= (character \- (digit | \*(Aq#\*(Aq)) {character \- \*(Aq#\*(Aq}
\&
\& directive      ::= todo_directive | skip_directive
\&
\& todo_directive ::= hash_mark \*(AqTODO\*(Aq \*(Aq \*(Aq {character}
\&
\& skip_directive ::= hash_mark \*(AqSKIP\*(Aq \*(Aq \*(Aq {character}
\&
\& comment        ::= hash_mark {character}
\&
\& hash_mark      ::= \*(Aq#\*(Aq {\*(Aq \*(Aq}
\&
\& bailout        ::= \*(AqBail out!\*(Aq {character}
\&
\& unknown        ::= { (character \- "\en") }
\&
\& (* POSIX character classes and other terminals *)
\&
\& digit              ::= [:digit:]
\& character          ::= ([:print:] \- "\en")
\& positiveInteger    ::= ( digit \- \*(Aq0\*(Aq ) {digit}
\& nonNegativeInteger ::= digit {digit}
.Ve
.SH "SUBCLASSING"
.IX Header "SUBCLASSING"
Please see \*(L"\s-1SUBCLASSING\*(R"\s0 in TAP::Parser for a subclassing overview.
.PP
If you \fIreally\fR want to subclass TAP::Parser's grammar the best thing to
do is read through the code.  There's no easy way of summarizing it here.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
TAP::Object,
TAP::Parser,
TAP::Parser::Iterator,
TAP::Parser::Result,