Jison grammar to convert numerals into an integer

gistfile1.c

/* Jison grammar for converting numerals into an integer */

/* The lexical analyzer 
   How we break things up into tokens */

%lex
%%

[0-9]+                  return 'INT'
"-"                     return '-'
<<EOF>>                 return 'EOF'
.                       return 'TOTAL_DISASTER'

/lex

%left UMINUS

/* The grammar
   How we figure out what the tokens mean */

%start grammar
%%

grammar
    : integer EOF                   { return $integer; }
    | EOF                           { return null; }
    ;

integer
    : INT                           { $$ = Number(yytext); }
    | '-' integer %prec UMINUS      { $$ = -$2; }
    ;