printSign :: Sign -> Doc
printSign s = printNodes "subjects:" (subjects s)
    $+$ printNodes "predicates:" (predicates s)
    $+$ printNodes "objects:" (objects s)
printSign :: Sign -> Doc
printSign s = printNodes "subjects:" (subjects s)
    $+$ printNodes "predicates:" (predicates s)
    $+$ printNodes "objects:" (objects s)
printSign s = printNodes "subjects:" (subjects s)
    $+$ printNodes "predicates:" (predicates s)
    $+$ printNodes "objects:" (objects s)