title: Library not found for -lfl
body: <p>I was using <code>flex</code> and <code>bison</code> to build a simple calculator project I cloned from Github.</p>
  
  <p>But after I typed <code>make</code> in terminal, I got the following message:</p>
  
  <pre><code>gcc -o calc calc.tab.c lex.yy.c -lfl
  calc.y:48:1: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
  main() {
  ^~~~
  1 warning generated.
  ld: library not found for -lfl
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  make: *** [calc] Error 1
  </code></pre>
  
  <p>How could I resolve this problem?</p>