<html><head><meta name="color-scheme" content="light dark"></head><body><pre style="word-wrap: break-word; white-space: pre-wrap;">% Copyright 2012-2022, Alexander Shibakov
% This file is part of SPLinT
%
% SPLinT is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% SPLinT 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 General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with SPLinT.  If not, see &lt;http://www.gnu.org/licenses/&gt;.

% assigning symbolic names to production terms (this is only a demonstration)

\def\makesymbols{%
      \restorecslist{symbols}\yyunion
      \toksa{}\toksb{}\toksc{}\toksd{}%
      \the\table
      \global\newsymswitch\newsymswitch
}

% symbolic reference name parser

\newtoks\newsymswitch
\newread\symnames

\newwrite\symbolicswitch

\def\inamespace{[intermediate]}%
\let\parsernamespace\inamespace
\let\hostparsernamespace\mainnamespace % purely for testing reasons
\pinittoks{}%
\input ptab.tex % this is the enhanced expression parser
\edef\tointermediateparser{%
    \let\noexpand\parsernamespace\noexpand\inamespace % switch to the new namespace
    \the\pinittoks % restore all the tables, tokens and constants, and stacks
    \let\noexpand\getcurrentparser\noexpand\tointermediateparser
}%
\settokens % this simply assigns values to tokens where the name of each token is taken out of yytname ...
\input xxpression.tok                     % this will set up token equivalences in the namespace above ...
                                          % those are the values gleaned during the bootstrapping stage.
                                          % in the general case, one needs to run a bootsrapping (or similar)
                                          % parser to extract the token information.
                                          % this is only needed if the bison file contains a definition that
                                          % lists both the idenitifier and a string as names for a token but the grammar
                                          % uses the identifier version at least once:
                                          % (say, %token IDENTIFIER "identifier"; is used as well as
                                          %       ...
                                          %       token:
                                          %           IDENTIFIER       { ... }
                                          %       ...
                                          %  see the included xxpression.w)
\optimizeall % this is necessary for correct rule listing in the output stage:
             % otherwise \fgetelemof will use the current value of the \yy... token registers which
             % will hold the values of the full parser that is loaded next
\newsymswitch{}%
\listrules                                % ... to be used while listing the rules
% note that we do not bother to set up a lexer for this parser (even though we already have one and the
% \optimizeall macro above will create a set of associative tables for it---this is merely an unwanted
% sideffect); after the rules have been listed, the intemediate parser in no longer needed.
%\showthe\newsymswitch
\def\fullnamespace{[full]}% this is the parser that parses the bison grammar from a raw
                          % bison file; it can play a role of the bootstrap parser for
                          % the grammar above, as well, since its input is a complete
                          % bison file; note that it cannot be a bootstrap parser for itself
                          % because it will reject any input that does not form a complete
                          % bison file; this is why a special grammar was created that includes
                          % only a small subset of the full set of productions (%token rules only) to
                          % serve as a bootstrap grammar.
%\tomainparser % this will set the value of \setflexstates, so that, if the lexer initialization
               % below is omitted, the \setflexstates macro can still be used to correctly set the
               % lexer states
\let\parsernamespace\fullnamespace
\pinittoks{}% %%
\input cweb/fyytab.tex
\input cweb/ltab.tex % we reinitialize the lexer out of necessity:
                                      % \collecttokennames needs to know how to switch
                                      % between two lexer/parser environments so both states
                                      % have to be preserved; if one is sure that
                                      % grammar_declarations will not used in the productions
                                      % part of the file, this can simply be disabled
\settokens
\setflexstates % the main lexer can be reused in this case; the states still need to be set up
\input bo.tok % set up the tokens for the bison grammar parser
\newparserstate
\newlexerstate
\newlexerstateextra
%
\setnulstack{yyirulestack}%
%
\edef\tofullparser{%
    \let\noexpand\parsernamespace\noexpand\fullnamespace % switch to the new namespace
    \the\pinittoks % restore all the tables, tokens and constants, and stacks
    \let\noexpand\getcurrentparser\noexpand\tofullparser
}%
\optimizeall
\toksa{\input xxpp.y}% start building the parsing command
                   % this has to be done carefully, since all the characters input
                   % from the parser file have to be `harmless', so their categories
                   % have to be reset; in order for the parser to be able to stop,
                   % appropriate command sequences would have to be inserted at the end
\toksb{\yyeof\yyeof\endparseinput\endparse
    \let\yyinput\yyinputold
    \undoascii
    \ifyyparsefail
        \errmessage{could not process symbols}%
    \else  
        \tointermediateparser % the parsing is finished, so we have two very long strings:
                              %  o the rules of the hosted parser ([intermediate])
                              %  o the rules of the same parser just parsed
                              % these two strings are used to associate the symbolic names
                              % (which only exist in the second list) to the rule numbers and
                              % the relevant terms;
                              % switching the parse namespace above is done so that the term
                              % indices are looked up in the appropriate table
        %\showthe\table
        \makesymbols % list all the rules deriving explicit non-terminals
        %\showthe\newsymswitch
        \setexplicitinlinerules\newsymswitch % process implicit non-terminals resulting from inline actions
        %\showthe\newsymswitch
        \makesymrefs\newsymswitch % create the switch to be used by the parser (\yyparse)
    \fi
}%
% build the command to create the symbolic name switch
\toksc{\tofullparser\basicparserinit\bisonparserinit\bisonparserdatainit
    \let\yyinputold\yyinput
    \let\yyinput\yyinputtrivial % a demo of a stripped down, slightly faster input routine
    \doascii{11}\expandafter\yyparse}%
\edef\next{\the\toksc\the\toksa\relax\the\toksb}\next % \relax is to stop \TeX\ from trying to expand the file name further
                                                      % it is not flagged as a bad character  because it is part of the epilogue
\immediate\openout\symbolicswitch=\jobname.sns
%
\edef\next{\setsncommands{\def\noexpand\symswitch\hashletter1{\harmlesscomment^^J\noexpand\ifcase\hashletter1\relax
                                                                       \harmlesscomment^^J\the\setsncommands
                                                                       \noexpand\else\harmlesscomment^^J%
                                                                       \noexpand\fi\harmlesscomment^^J%
                                                                       }\harmlesscomment^^J^^J}}\next
\edef\next{\unsetsncommands{\def\noexpand\symswitchoff\hashletter1{\harmlesscomment^^J\noexpand\ifcase\hashletter1\relax
                                                                       \harmlesscomment^^J\the\unsetsncommands
                                                                       \noexpand\else\harmlesscomment^^J%
                                                                       \noexpand\fi\harmlesscomment^^J%
                                                                       }\harmlesscomment^^J^^J}}\next
{\newlinechar=`\^^J \immediate\write\symbolicswitch{\the\setsncommands\the\unsetsncommands}}%
\immediate\closeout\symbolicswitch
\tomainparser % go back to the main parser

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