pascal.lex

flex

/*
 * pascal.lex: An example PASCAL scanner
 *
 */

%{
#include <stdio.h>
#include "y.tab.h"

int line_number = 0;

void yyerror(char *message);

%}

%x COMMENT1 COMMENT2

white_space       [ \t]*
digit             [0-9]
alpha             [A-Za-z_]
alpha_num         ({alpha}|{digit})
hex_digit         [0-9A-F]
identifier        {alpha}{alpha_num}*
unsigned_integer  {digit}+
hex_integer       ${hex_digit}{hex_digit}*
exponent          e[+-]?{digit}+
i                 {unsigned_integer}
real              ({i}\.{i}?|{i}?\.{i}){exponent}?
string            \'([^'\n]|\'\')+\'
bad_string        \'([^'\n]|\'\')+

%%

"{"                  BEGIN(COMMENT1);
<COMMENT1>[^}\n]+
<COMMENT1>\n            ++line_number;
<COMMENT1><<EOF>>    yyerror("EOF in comment");
<COMMENT1>"}"        BEGIN(INITIAL);

"(*"                 BEGIN(COMMENT2);
<COMMENT2>[^)*\n]+
<COMMENT2>\n            ++line_number;
<COMMENT2><<EOF>>    yyerror("EOF in comment");
<COMMENT2>"*)"       BEGIN(INITIAL);
<COMMENT2>[*)]

 /* note that FILE and BEGIN are already 
  * defined in FLEX or C so they can't  
  * be used. This can be overcome in                               
  * a cleaner way by defining all the
  * tokens to start with TOK_ or some
  * other prefix.
  */

and                  return(AND);
array                return(ARRAY);
begin                return(_BEGIN);
case                 return(CASE);
const                return(CONST);
div                  return(DIV);
do                   return(DO);
downto               return(DOWNTO);
else                 return(ELSE);
end                  return(END);
file                 return(_FILE);
for                  return(FOR);
function             return(FUNCTION);
goto                 return(GOTO);
if                   return(IF);
in                   return(IN);
label                return(LABEL);
mod                  return(MOD);
nil                  return(NIL);
not                  return(NOT);
of                   return(OF);
packed               return(PACKED);
procedure            return(PROCEDURE);
program              return(PROGRAM);
record               return(RECORD);
repeat               return(REPEAT);
set                  return(SET);
then                 return(THEN);
to                   return(TO);
type                 return(TYPE);
until                return(UNTIL);
var                  return(VAR);
while                return(WHILE);
with                 return(WITH);

"<="|"=<"            return(LEQ);
"=>"|">="            return(GEQ);
"<>"                 return(NEQ);
"="                  return(EQ);

".."                 return(DOUBLEDOT);

{unsigned_integer}   return(UNSIGNED_INTEGER);
{real}               return(REAL);
{hex_integer}        return(HEX_INTEGER);
{string}             return{STRING};
{bad_string}         yyerror("Unterminated string");

{identifier}         return(IDENTIFIER);

[*/+\-,^.;:()\[\]]   return(yytext[0]);

{white_space}        /* do nothing */
\n                   line_number += 1;
.                    yyerror("Illegal input");

%%

void yyerror(char *message)
{
   fprintf(stderr,"Error: \"%s\" in line %d. Token = %s\n",
           message,line_number,yytext);
   exit(1);
}