FLEX - Grammar language

FLEX is an open source grammar language created in 1987 by Vern Paxson.

#247on PLDB

37Years Old

Download source code:

git clone https://github.com/westes/flex

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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...

Tags: grammarLanguage
FLEX is developed on GitHub and has 3,518 stars
Early development of FLEX happened in University of California Berkeley
FLEX is written in Lex, C, Bourne shell, Make, Yacc, LLVM IR, M4, Markdown, YAML, Perl, awk, C++, IDL
FLEX on HOPL
See also: (5 related languages) Bison, Yacc, C, RATFOR, PL/0
Read more about FLEX on the web: 1.

Example from Riju:

%{
#include <stdio.h>
%}

%%
%%

int yywrap() {
  printf("Hello, world!\n");
  return 1;
}

int main() {
  yylex();
  return 0;
}

Example 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;}