--- a/progs/roman_sol.scala	Wed Jan 25 17:23:00 2017 +0000
+++ b/progs/roman_sol.scala	Thu Jan 26 01:43:31 2017 +0000
@@ -1,3 +1,6 @@
+// Part 1 about Roman Numerals
+//=============================
+
 abstract class RomanDigit 
 case object I extends RomanDigit 
 case object V extends RomanDigit 
@@ -9,6 +12,12 @@
 
 type RomanNumeral = List[RomanDigit] 
 
+
+// (1) First write a polymorphic function that recursively
+// transforms a list of options into an option of a list.
+// As soon as a None is inside the list, the result is None. 
+// Otherwise produce a list of all Some's appended.
+
 def optionlist[A](xs: List[Option[A]]): Option[List[A]] = xs match {
   case Nil => Some(Nil)
   case x::xs => (x, optionlist(xs)) match {
@@ -18,7 +27,16 @@
   }
 }
 
-def char2romandigit(c: Char): Option[RomanDigit] = c match {
+optionlist(List(Some(1), Some(2), Some(3)))
+optionlist(List(Some(1), None, Some(3)))
+optionlist(List())
+
+// (2) Write a function first a function that converts a character
+// into a roman digit (if possible). Then convert a string into
+// a roman numeral (if possible). If this is not possible, the functions
+// should return None.
+
+def Char2RomanDigit(c: Char): Option[RomanDigit] = c match {
   case 'I' => Some(I)
   case 'V' => Some(V)
   case 'X' => Some(X)
@@ -30,8 +48,9 @@
 }
 
 def String2RomanNumeral(s: String) : Option[RomanNumeral] = 
-  optionlist(s.toList.map(char2romandigit))
+  optionlist(s.toList.map(Char2RomanDigit))
 
+// some test cases
 String2RomanNumeral("IIII")
 String2RomanNumeral("IV")
 String2RomanNumeral("VI")
@@ -40,7 +59,9 @@
 String2RomanNumeral("MCMXLIV") 
 String2RomanNumeral("M C M X L I V")  // None
 
-////////////////
+
+// (3) Write a recursive function RomanNumral2Int that converts a
+// RomanNumeral into an integer.
 
 def RomanNumeral2Int(rs: RomanNumeral): Int = rs match { 
   case Nil => 0
@@ -59,6 +80,7 @@
   case I::r    => 1 + RomanNumeral2Int(r)
 }
 
+// some test cases
 RomanNumeral2Int(List(I,I,I,I))         // 4
 RomanNumeral2Int(List(I,V))             // 4
 RomanNumeral2Int(List(V,I))             // 6
@@ -67,6 +89,10 @@
 RomanNumeral2Int(List(M,C,M,X,L,I,V))   // 1944
 
 
+// (4) Write a function that converts a string (containing
+// a roman numeral) into an integer (if possible). If not
+// this is not possible, the functions should return None.
+
 def String2Int(s: String): Option[Int] = 
   String2RomanNumeral(s).map(RomanNumeral2Int(_))
 
@@ -106,13 +132,34 @@
 String2Int("CIM") 	// ?? 899
 String2Int("MDCLXVI")	// 1666
 
-String2Int("VIV")       //9, but should be written as IX 
+String2Int("VIV")       // 9, but should be written as IX 
 String2Int("IVX")       // 14 invalid
 
 // error cases
 String2Int("MC?I")
 String2Int("abc")
 
+// (5) The file roman.txt contains a list of roman numerals. 
+// Read in these numerals, convert them into integers and then 
+// add them all up.
+
+import io.Source
+import scala.util._
+
+// function for reading files:
+// Source.fromFile("file_name")("ISO-8859-9")
+
+def addromanfile(filename: String) = {
+  val lines = Source.fromFile(filename)("ISO-8859-9").getLines.toList.map(_.trim)
+  lines.map(String2Int(_)).flatten.sum
+}
+
+
+addromanfile("roman.txt")
+
+
+
+
 
 def runsAllowed(r: RomanDigit) = r match {
   case I | X | C | M => true