sub bool_to_regexp
{
        local($query) = @_;
        # Sanity check: query must not contain unescaped "/"!
        $query =~ s|^/|\\/|;
        $query =~ s|([^\\])/|\\/|g;

        # boolean expression (or single word)
        local($not, $join);
        #local($qrycmd) = "next unless (";
        local($qrycmd) = "";

        # $query =~ tr/A-Z/a-z/;

        $query =~ s/\(/ ( /g;   # make sure brackets are separate "words"
        $query =~ s/\)/ ) /g;
        $query =~ s/["'`]//g;   # quotes don't work (yet?)

        # for (split(/[+ \t]+/, $query)) {
        # Splitting on "+" is bad for queries like "C++"!

        $query =~ s/\+/\\+/g;
        for (split(/[ \t]+/, $query)) {
                # for each "word", do ...
                next if /^$/;
                if ($_ eq ")") { $qrycmd .= $_; next; }
                if ($_ eq "(") { $qrycmd .= "$join$_"; $join = ""; next; }
                if ($_ eq "NOT") { $not = "!"; next; }
                if ($_ eq "OR")  { $join = " || "; next; }
                if ($_ eq "AND") { $join = " && "; next; }
                if (/\*/)
                {
                  s/\*/\\w*/g;
                }

                # match word boundaries only if fully alphanumeric
                # (for queries like "C++")

                elsif (/^\w+$/)
                {
                  s/(.*)/\\b\1\\b/;
                }

                $qrycmd .= "$join $not/$_/$caseSensitivity";
                $join = " && "; # default to AND joins
                $not = "";
        }
        $qrycmd .= "";
}