loop {
  var expr = Sys.readln("\nBoolean expression (e.g. 'a & b'): ").strip.lc
  break if expr.is_empty;

  var vars = expr.scan(/[[:alpha:]]+/)
  if (vars.is_empty) {
    say "no variables detected in your boolean expression"
    next
  }

  var prefix = [];
  var suffix = [];

  vars.each { |v|
    print "#{v}\t"
    prefix << "[false, true].each { |#{v}|"
    suffix << "}"
  }
  say "| #{expr}"

  var body = ("say (" + vars.map{|v| v+",'\t'," }.join + " '| ', #{expr})")
  eval(prefix + [body] + suffix -> join("\n"))
}