Lex Help

I am trying to implement a simple program in LEX but it is giving error.
I am doing it in Ubuntu.

Code:

%{
#include <stdio.h>
%}

digit         [0-9]
letter        [A-Za-z]


%%
    /*** Rules section ***/

   {letter} { return 1; }

%%
/*** C Code section ***/

int main(void)
{
    /* Call the lexer, then quit. */
    yylex();
    return 0;
}

Code:

text.lex: In function ‘yylex’:
text.lex:13: error: ‘letter’ undeclared (first use in this function)
text.lex:13: error: (Each undeclared identifier is reported only once
text.lex:13: error: for each function it appears in.)
text.lex:13: error: expected ‘;’ before ‘}’ token

I'm using [ ] instead of curly braces so it doesn't whine about code tags...
Move [letter] all the way to the left column on line 13. It thinks you're trying to match nothing/everything, and produce two pieces of code, one with [letter] and one with [ return 1; ]

Thanks it worked!