scc-lexer.l

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%{
// This file contains all the rules that GNU Flex needs to identify tokens in
// the script source code.  GNU Flex is a lexical analyzer (or lexer) that
// finds tokens in the input stream.  Flex is a tool that is commonly used in
// conjunction with GNU Bison and more information about this tool can be
// found at:   http://www.gnu.org/software/flex/

#include "SCC.H"
#include "PTNode.H"
#include "scc-parser.h"

// NOTE: The C-style comments below are intentional.  Flex does not like
// C++-style comments inside of its rules definitions below.  Also, you want
// to make sure that the comment does not start in the first column.  Flex
// does not have any way to know distinguish between the /* comment and the
// regular expression /*


// The symbol table is externed in SCC.H, so we need to simply allocate the
// space for it here.
SymbolTable symtbl;

// This function will called by the lexer when it encounters an identifier.
// It handles returning the proper data to the parser.
int GetIdentifier();

%}


  /* Define the regular expressions for comments, whitespace, and numbers. */
comment             \/\/.*$
ws                  [\r\n\t ]+
number              [0-9]+
identifier          [_a-zA-Z][_a-zA-Z0-9]*

 /* This option tells Flex that this script is never ran interactively.  This
  * is needed for Windows builds since a few UNIX functions are not
  * implemented by Microsoft. */
%option never-interactive


%%


{comment}           /* comments are ignored */
{ws}                /* whitespace is ignored */

{number}            {
                       /* This rule matches any integer found in the input
                        * stream.  The matched text will be in the yytext
                        * string, and we need to convert it to an integer.
                        * After this is done, create a new constant parse tree
                        * node and return this node to the parser.  This is
                        * done through the Bison-defined variable 'yylval'. */

                      int value = strtol( yytext, NULL, 0 );
                      yylval = new ConstantNode( value );

                      return NUMBER;
                    }

"else"              return K_ELSE;
"for"               return K_FOR;
"if"                return K_IF;

{identifier}        return GetIdentifier();

 /* This regular expression returns any character that was not matched by a
  * rule above to the parser.  This allows the parser to understand the single
  * letter tokens such as + and - */
.           return yytext[0];


%%


// Flex requires that this function is defined.  It will call this function
// whenever it reaches the end of the input stream.  If this function returns
// 1, then Flex will terminate reading.  This function is commonly used to
// switch to another file when the current one is finished (for example, the
// user entered two scripts on the command line).
int yywrap()
{
  return 1;
}


int
GetIdentifier()
{
  // This function needs to inform the parser that we have encountered an
  // identififer.  For newly encountered variables, a new identifier node to
  // track the variable and it is stuffed into the symbol table.  When the
  // variable is encountered again, the previously allocated identifier node
  // is returned.  This ensures that the parser only sees one pointer per
  // variable.

  string name = yytext;
  SymbolTable::iterator i = symtbl.find( name );

  if ( i == symtbl.end() ) {
    IdentifierNodePtr identifier = new IdentifierNode( name );
    symtbl.insert( SymbolTable::value_type( name, identifier ) );

    yylval = identifier;
  } else {
    yylval = (*i).second;
  }

  return IDENTIFIER;
}