diff -r 99dcfdf5aed8 -r f51e593903ac progs/lecture2.scala
--- a/progs/lecture2.scala	Thu Nov 17 20:05:36 2022 +0000
+++ b/progs/lecture2.scala	Mon Nov 21 15:57:45 2022 +0000
@@ -70,14 +70,19 @@
 // List[Int]: Nil, List(_) 
 //
 // Option[Int]: None, Some(0), Some(1), ...
+// Option[Boolean]: None, Some(true), Some(false)
 // Option[...]: None, Some(_)
 
 def safe_div(x: Int, y: Int) : Option[Int] = 
   if (y == 0) None else Some(x / y)
 
-List(1,2,3,4,5,6).indexOf(7)
+safe_div(10 + 5, 4 - 1)  
 
-def my_min(ls: List[Int]) : Option[Int] = ls.minOption
+List(1,2,3,4,5,6).indexOf(7)
+List[Int]().minOption
+
+def my_min(ls: List[Int]) : Option[Int] = 
+  ls.minOption
 
 my_min(List(1,2,3,4))
 
@@ -90,9 +95,10 @@
 import scala.util._
 import io.Source
 
-val my_url = "https://nms.kcl.ac.uk/christian.urban2/"
+val my_url = "https://nms.kcl.ac.uk/christian.urban/"
 
 Source.fromURL(my_url)("ISO-8859-1").mkString
+Source.fromURL(my_url)("ISO-8859-1").getLines().toList
 
 Try(Source.fromURL(my_url)("ISO-8859-1").mkString).getOrElse("")
 
@@ -100,14 +106,18 @@
 
 
 // the same for files
+
 Try(Some(Source.fromFile("test.txt")("ISO-8859-1").mkString)).getOrElse(None)
 
+Try(Source.fromFile("test.txt")("ISO-8859-1").mkString).toOption
+
+Using(Source.fromFile("test.txt")("ISO-8859-1"))(_.mkString).toOption
 
 // how to implement a function for reading 
-// (lines) something from files...
+// (lines) from files...
 //
 def get_contents(name: String) : List[String] = 
-  Source.fromFile(name)("ISO-8859-1").getLines.toList
+  Source.fromFile(name)("ISO-8859-1").getLines().toList
 
 get_contents("text.txt")
 get_contents("test.txt")
@@ -120,7 +130,7 @@
 
 // much better - you record in the type that things can go wrong 
 def get_contents(name: String) : Option[List[String]] = 
-  Try(Some(Source.fromFile(name)("ISO-8859-1").getLines.toList)).getOrElse(None)
+  Try(Some(Source.fromFile(name)("ISO-8859-1").getLines().toList)).getOrElse(None)
 
 get_contents("text.txt")
 get_contents("test.txt")
@@ -158,8 +168,6 @@
 val lst = List(None, Some(1), Some(2), None, Some(3))
 
 
-
-
 // a function that turns strings into numbers 
 // (similar to .toInt)
 Integer.parseInt("1234")
@@ -234,7 +242,7 @@
 lst.find(n => odd(n) && n > 2)
 
 
-
+// lexicographic ordering
 val ps = List((3, 0), (3, 2), (4, 2), (2, 2), 
               (2, 0), (1, 1), (1, 0))