diff -r 5e070fb0332a -r eda0ccf56c72 progs/parser-combinators/comb1.sc
--- a/progs/parser-combinators/comb1.sc	Sat Nov 04 18:28:09 2023 +0000
+++ b/progs/parser-combinators/comb1.sc	Sat Nov 11 10:08:33 2023 +0000
@@ -20,6 +20,7 @@
         if is(tl).isEmpty) yield hd
 }
 
+
 // parser combinators
 
 
@@ -39,7 +40,7 @@
 
 // map parser
 class MapParser[I : IsSeq, T, S](p: => Parser[I, T], 
-                         f: T => S) extends Parser[I, S] {
+                                 f: T => S) extends Parser[I, S] {
   def parse(in: I) = for ((hd, tl) <- p.parse(in)) yield (f(hd), tl)
 }
 
@@ -51,7 +52,11 @@
     if (in != "" && in.head == c) Set((c, in.tail)) else Set()
 }
 
-CharParser('a').parse("abc")
+val ap = CharParser('a')
+val bp = CharParser('b')
+
+val abp = SeqParser(ap, bp)
+MapParser(abp, ab => s"$ab").parse("abc")
 
 // an atomic parser for parsing strings according to a regex
 import scala.util.matching.Regex
@@ -67,14 +72,14 @@
 val NumParser = RegexParser("[0-9]+".r)
 def StrParser(s: String) = RegexParser(Regex.quote(s).r)
 
-NumParser.parse("a123a123bc") 
+NumParser.parse("123a123bc") 
 StrParser("else").parse("elsethen")
 
 
 // NumParserInt transforms a "string integer" into a propper Int
 // (needs "new" because MapParser is not a case class)
 
-val NumParserInt = new MapParser(NumParser, (s: String) => s.toInt)
+val NumParserInt = MapParser(NumParser, (s: String) => s.toInt)
 NumParserInt.parse("123abc")
 
 // the following string interpolation allows us to write 
@@ -111,6 +116,7 @@
 
 val NumParserInt2 = NumParser.map(_.toInt)
 
+val x = 1 + 3
 
 // A parser for palindromes (just returns them as string)
 //  since the parser is recursive it needs to be lazy
@@ -121,8 +127,8 @@
 }  
 
 // examples
-Pal.parse_all("abaaaba")
-Pal.parse("abaaaba")
+Pal.parse_all("abacaba")
+Pal.parse("abacaaba")
 
 println("Palindrome: " + Pal.parse_all("abaaaba"))
 
@@ -143,6 +149,9 @@
 
 // A parser for arithmetic expressions (Terms and Factors)
 
+"1 + 2 * 3"
+"(1 + 2) * 3"
+{
 lazy val E: Parser[String, Int] = {
   (T ~ p"+" ~ E).map{ case ((x, _), z) => x + z } ||
   (T ~ p"-" ~ E).map{ case ((x, _), z) => x - z } || T }
@@ -150,12 +159,12 @@
   (F ~ p"*" ~ T).map{ case ((x, _), z) => x * z } || F }
 lazy val F: Parser[String, Int] = {
   (p"(" ~ E ~ p")").map{ case ((_, y), _) => y } || NumParserInt }
-
+}
 println(E.parse_all("1+3+4"))
 println(E.parse("1+3+4"))
 println(E.parse_all("4*2+3"))
 println(E.parse_all("4*(2+3)"))
-println(E.parse_all("(4)*((2+3))"))
+println(E.parse_all("(4)*(((2+3)))"))
 println(E.parse_all("4/2+3"))
 println(E.parse("1 + 2 * 3"))
 println(E.parse_all("(1+2)+3"))