var sq = syntax (e1=token ["a"] e2=token ["b"] {Seq (e1, e2)}),
      al = syntax (e=(token ["a"] | token ["b"]) {Alt (e)}),
      rp = syntax (e=token ["a"]* {Rep (e)});

printf ("%s\n", parseString (syntax (p=sq eof {p}), "ab").string);
printf ("%s\n", parseString (syntax (p=al eof {p}), "a").string);
printf ("%s\n", parseString (syntax (p=al eof {p}), "b").string);
printf ("%s\n", parseString (syntax (p=rp eof {p}), "aaa").string)