diff -r c7009356ddd8 -r c0600f8b6427 solutions/cw4/parser.sc
--- a/solutions/cw4/parser.sc	Wed May 29 13:25:30 2024 +0100
+++ b/solutions/cw4/parser.sc	Thu Sep 19 15:47:33 2024 +0100
@@ -1,13 +1,14 @@
 // CW3
 
-import $file.lexer
-import lexer._ 
+import scala.language.implicitConversions
+
+import $file.lexer, lexer._ 
 
 case class ~[+A, +B](x: A, y: B)
 
 // parser combinators
 
-abstract class Parser[I, T](using is: I => Seq[_])  {
+abstract class Parser[I, T](using is: I => Seq[?])  {
   def parse(in: I): Set[(T, I)]  
 
   def parse_all(in: I) : Set[T] =
@@ -17,13 +18,13 @@
 
 // alternative parser
 class AltParser[I, T](p: => Parser[I, T], 
-                      q: => Parser[I, T])(using I => Seq[_]) extends Parser[I, T] {
+                      q: => Parser[I, T])(using I => Seq[?]) extends Parser[I, T] {
   def parse(in: I) = p.parse(in) ++ q.parse(in)   
 }
 
 // sequence parser
 class SeqParser[I, T, S](p: => Parser[I, T], 
-                         q: => Parser[I, S])(using I => Seq[_]) extends Parser[I, ~[T, S]] {
+                         q: => Parser[I, S])(using I => Seq[?]) extends Parser[I, ~[T, S]] {
   def parse(in: I) = 
     for ((hd1, tl1) <- p.parse(in); 
          (hd2, tl2) <- q.parse(tl1)) yield (new ~(hd1, hd2), tl2)
@@ -31,14 +32,14 @@
 
 // map parser
 class MapParser[I, T, S](p: => Parser[I, T], 
-                         f: T => S)(using I => Seq[_]) extends Parser[I, S] {
+                         f: T => S)(using I => Seq[?]) extends Parser[I, S] {
   def parse(in: I) = for ((hd, tl) <- p.parse(in)) yield (f(hd), tl)
 }
 
 // more convenient syntax for parser combinators
-extension [I, T](p: Parser[I, T])(using I => Seq[_]) {
+extension [I, T](p: Parser[I, T])(using I => Seq[?]) {
   def ||(q : => Parser[I, T]) = new AltParser[I, T](p, q)
-  def ~[S] (q : => Parser[I, S]) = new SeqParser[I, T, S](p, q)
+  def ~[S] (q : => Parser[I, S])(using S => Seq[?]) = new SeqParser[I, T, S](p, q)
   def map[S](f: => T => S) = new MapParser[I, T, S](p, f)
 }
 
@@ -71,16 +72,18 @@
 
 // Implicit definitions to go from a token 
 // or a list of tokens to a TokenListParser
-implicit def token2parser(t: Token) : Parser[List[Token], Token] = 
-  TokenParser(t)
+given Conversion[Token, Parser[List[Token], Token]] = (t => TokenParser(t))
+//implicit def token2parser(t: Token) : Parser[List[Token], Token] = 
+//  TokenParser(t)
 
+/*
 extension (t: Token) {
     def || (q : => Parser[List[Token], Token]) = 
       new AltParser[List[Token], Token](t, q)
     def ~[S](q : => Parser[List[Token], S]) = 
       new SeqParser[List[Token], Token, S](t, q)  
 }
-
+*/
 
 
 // Abstract Syntax Trees