diff -r 9d4c5abff8c5 -r 4e254e201ce9 progs/comb1a.scala
--- a/progs/comb1a.scala	Sun Oct 27 11:57:57 2019 +0000
+++ b/progs/comb1a.scala	Sun Oct 27 13:03:58 2019 +0000
@@ -65,7 +65,7 @@
 implicit def string2parser(s: String) = StringParser(s)
 implicit def char2parser(c: Char) = CharParser(c)
 
-implicit def ParserOps[I, T](p: Parser[I, T])(implicit ev: I => Seq[_]) = new {
+implicit def ParserOps[I : IsSeq, T](p: Parser[I, T]) = new {
   def || (q : => Parser[I, T]) = new AltParser[I, T](p, q)
   def ==>[S] (f: => T => S) = new FunParser[I, T, S](p, f)
   def ~[S] (q : => Parser[I, S]) = new SeqParser[I, T, S](p, q)