formatStmt (Swap id1 id2 _) =
  formatIdent id1 <+> text "<=>" <+> formatIdent id2
formatStmt (Swap id1 id2 _) =
  formatIdent id1 <+> text "<=>" <+> formatIdent id2
formatStmt (Swap id1 id2 _) =
  formatIdent id1 <+> text "<=>" <+> formatIdent id2