On 21/09/2010 06:32, Arno Trautmann wrote:
>> Why not just use&&  in the first place?
>
> Because of possible catcode-troubles? ;)
> Or maybe such a list might be more useful for a xor operation.

How does the following look? The Boolean expressions are the most basic 
versions (NOT takes one argument, others take two), but nesting seems to 
work fine. There is definitely less code to this than the current 
implementation, so there would be a performance gain.

\documentclass{article}
\usepackage{expl3}
\ExplSyntaxOn
\cs_set_nopar:Npn \bool_if:nT #1 {
   \tex_ifodd:D \bool_if_p:n {#1}
     \tex_expandafter:D \use:n
   \tex_else:D
     \tex_expandafter:D \use_none:n
   \tex_fi:D
}
\cs_set_nopar:Npn \bool_if:nF #1 {
   \tex_ifodd:D \bool_if_p:n {#1}
     \tex_expandafter:D \use_none:n
   \tex_else:D
     \tex_expandafter:D \use:n
   \tex_fi:D
}
\cs_set_nopar:Npn \bool_if:nTF #1 {
   \tex_ifodd:D \bool_if_p:n {#1}
     \tex_expandafter:D \use_i:nn
   \tex_else:D
     \tex_expandafter:D \use_ii:nn
   \tex_fi:D
}
\cs_set_nopar:Npn \bool_if_p:n #1 {
   \tex_number:D #1 ~
}
\cs_set_nopar:Npn \bool_not_p:n #1 {
   \tex_ifnum:D \tex_number:D #1 = \c_true_bool
     \c_false_bool
   \tex_else:D
     \c_true_bool
   \tex_fi:D
}
\cs_set_nopar:Npn \bool_and_p:nn #1#2 {
   \tex_ifnum:D \tex_number:D #1 = \c_true_bool
     \tex_ifnum:D \tex_number:D #2 = \c_true_bool
       \c_true_bool
     \tex_else:D
       \c_false_bool
     \tex_fi:D
   \tex_else:D
     \c_false_bool
   \tex_fi:D
}
\cs_set_nopar:Npn \bool_or_p:nn #1#2 {
   \tex_ifnum:D \tex_number:D #1 = \c_true_bool
     \c_true_bool
   \tex_else:D
     \tex_ifnum:D \tex_number:D #2 = \c_true_bool
       \c_true_bool
     \tex_else:D
       \c_false_bool
     \tex_fi:D
   \tex_fi:D
}
\cs_set_nopar:Npn \bool_xor_p:nn #1#2 {
   \tex_ifnum:D \tex_number:D #1 = \c_true_bool
     \tex_ifnum:D \tex_number:D #2 = \c_true_bool
       \c_false_bool
     \tex_else:D
       \c_true_bool
     \tex_fi:D
   \tex_else:D
     \tex_ifnum:D \tex_number:D #2 = \c_true_bool
       \c_false_bool
     \tex_else:D
       \c_true_bool
     \tex_fi:D
   \tex_fi:D
}
\ExplSyntaxOff
\begin{document}

\ExplSyntaxOn

\bool_if:nTF { \c_true_bool } { TRUE } { FALSE } ~
\bool_if:nTF { \bool_not_p:n { \c_true_bool } } { TRUE } { FALSE } ~
\bool_if:nTF
   {
    \bool_and_p:nn { \c_true_bool }
    {
      \bool_not_p:n { \bool_or_p:nn { \c_true_bool } { \c_false_bool } }
    }
   } { TRUE } { FALSE } ~

\bool_if:nTF
   {
    \bool_and_p:nn { \c_true_bool }
    {
      \bool_not_p:n { \bool_or_p:nn { \c_true_bool } { \c_false_bool } }
    }
   } { TRUE } { FALSE } ~

\bool_if:nTF { % LAZY EVALUATION
  \bool_and_p:nn
    { \int_compare_p:nNn { 1 } = { 1 } }
    {
      \bool_and_p:nn
        {
           \bool_if_p:n
             {
               \bool_or_p:nn
                 { \intexpr_compare_p:nNn { 2 } = { 3 } }
                 {
                   \bool_or_p:nn
                     { \intexpr_compare_p:nNn { 4 } = { 4 } }
                     { \intexpr_compare_p:nNn { 1 } = { \ERROR } } % Skip
                 }
             }
         }
         { \int_compare_p:nNn { 2 } = { 2 } }
     }
} { TRUE } { FALSE } ~

\ExplSyntaxOff
\end{document}
-- 
Joseph Wright