     input sequence every time it is requested.
            </p>
<p>
              But as soon as you specify at least one token value type while defining
              the token type you'll have to list all value types used for <code class="computeroutput"><span class="identifier">lex</span><span class="special">::</span><span class="identifier">token_def</span><span class="special">&lt;&gt;</span></code>
              declarations in the token definition class, otherwise compilation errors
              w