FLEX
FLEX is a grammar language created in 1987. Flex (fast lexical analyzer generator) is a free and open-source software alternative to lex. It is a computer program that generates lexical analyzers (also known as "scanners" or "lexers"). It is frequently used as the lex implementation together with Berkeley Yacc parser generator on BSD-derived operating systems (as both lex and yacc are part of POSIX), or together with GNU bison (a version of yacc) in *BSD ports and in Linux distributions. Read more on Wikipedia...
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- FLEX ranks in the top 25% of languages
- the FLEX website
- the FLEX wikipedia page
- FLEX first appeared in 1987
- See also: bison, yacc, c, ratfor, pl-0
- Have a question about FLEX not answered here? Email me and let me know how I can help.
Example code from Wikipedia:
%{
#include "y.tab.h"
%}
digit [0-9]
letter [a-zA-Z]
%%
"+" { return PLUS; }
"-" { return MINUS; }
"*" { return TIMES; }
"/" { return SLASH; }
"(" { return LPAREN; }
")" { return RPAREN; }
";" { return SEMICOLON; }
"," { return COMMA; }
"." { return PERIOD; }
":=" { return BECOMES; }
"=" { return EQL; }
"<>" { return NEQ; }
"<" { return LSS; }
">" { return GTR; }
"<=" { return LEQ; }
">=" { return GEQ; }
"begin" { return BEGINSYM; }
"call" { return CALLSYM; }
"const" { return CONSTSYM; }
"do" { return DOSYM; }
"end" { return ENDSYM; }
"if" { return IFSYM; }
"odd" { return ODDSYM; }
"procedure" { return PROCSYM; }
"then" { return THENSYM; }
"var" { return VARSYM; }
"while" { return WHILESYM; }
{letter}({letter}|{digit})* {
yylval.id = strdup(yytext);
return IDENT; }
{digit}+ { yylval.num = atoi(yytext);
return NUMBER; }
[ \t\n\r] /* skip whitespace */
. { printf("Unknown character [%c]\n",yytext[0]);
return UNKNOWN; }
%%
int yywrap(void){return 1;}
Last updated February 18th, 2020