I have a syntax definition with a proper pp file, and all installs fine. But when using the prettyprinter (abox2text) on a parsed example file, I receive an error. (All occurs in my TFOF package)

Example file:

module datatypes
  types
  data List a = Cons a (List a)
              | Nil


(relevant part of) SDF:

"data" ConId TypeVarId*
       "=" {(ConId Type*) "|"}+ -> TypeDef {cons("DataType")}

(Note the ConId Type* grouped to form the first argument of the iter-sep.


pp-rules (equal to pp-gen output, but enhanced by hand):

DataType -- H [KW["data"] _1 _2 H [KW["="] V[_3]]],
   DataType.2:iter-star -- _1,
   DataType.3:iter-sep -- H [_1 KW["|"]],
   DataType.3:iter-sep.1:seq -- H hs=1[_1 _2],
   DataType.3:iter-sep.1:seq.2:iter-star -- _1,


Now running the pretty-printer on the (correctly-parsed) example file produces:
  $ parse-tfof -i xmpl/datatypes.tfmd | ast2abox -p pp/TFOF-pretty.pp | abox2text
  No pp entry found for: (2,[""])
  ** ERROR: cannot rewrite to box: ("Nil",[])
  ast2abox: rewriting failed


Apparently the :seq pp-rule is not (properly) used.
A fix for now is to have in my SDF:

ConId Type* -> TypeKind {cons("TypeKind")}
    "data" ConId TypeVarId*
      "=" {TypeKind "|"}+ -> TypeDef {cons("DataType")}


The two :seq entries can be left out of the pp file now, an all works fine. But it still seems like tuples should be supported.