--- a/progs/knight2_sol.scala	Tue Nov 22 01:35:40 2016 +0000
+++ b/progs/knight2_sol.scala	Wed Nov 23 13:32:01 2016 +0000
@@ -43,11 +43,13 @@
     first(legal_moves(dim, path, path.head), (x: Pos) => first_tour(dim, x::path))
 }
 
+/*
 for (dim <- 1 to 8) {
   val t = first_tour(dim, List((0, 0)))
   println(s"${dim} x ${dim} " + (if (t == None) "" else { print_board(dim, t.get) ; "" }))
 }
+*/
  
+print_board(8, first_tour(8, List((0, 0))).get)
 
 
-

--- a/progs/knight3_sol.scala	Tue Nov 22 01:35:40 2016 +0000
+++ b/progs/knight3_sol.scala	Wed Nov 23 13:32:01 2016 +0000
@@ -31,7 +31,10 @@
 def ordered_moves(dim: Int, path: Path, x: Pos): List[Pos] = 
   legal_moves(dim, path, x).sortBy((x) => legal_moves(dim, path, x).length)
 
+import scala.annotation.tailrec
 
+/*
+@tailrec
 def first(xs: List[Pos], f: Pos => Option[Path]): Option[Path] = xs match {
   case Nil => None
   case x::xs => {
@@ -39,6 +42,10 @@
     if (result.isDefined) result else first(xs, f)
   }
 }
+*/
+
+def first[A, B](xs: List[A], f: A => Option[B]): Option[B] =
+  xs.flatMap(f(_)).headOption
 
 
 def first_closed_tour_heuristics(dim: Int, path: Path): Option[Path] = {
@@ -47,19 +54,46 @@
     first(ordered_moves(dim, path, path.head), (x: Pos) => first_closed_tour_heuristics(dim, x::path))
 }
 
+/*
 for (dim <- 1 to 6) {
   val t = first_closed_tour_heuristics(dim, List((dim / 2, dim / 2)))
   println(s"${dim} x ${dim} closed: " + (if (t == None) "" else { print_board(dim, t.get) ; "" }))
 }
+*/
+
+//@tailrec
+def first_tour_heuristics(dim: Int, path: Path): Option[Path] = {
+
+  @tailrec
+  def aux(dim: Int, path: Path, moves: List[Position]): Option[Path 
+  if (path.length == dim * dim) Some(path)
+  else
+    moves match {
+      case Nil => None
+      case x::xs => {
+        val r = first_tour_heuristics(dim, x::path)
+        if (r.isDefined) Some(r) else aux(dim, path, xs)
+    }    
+  aux(dim, path, ordered_moves(dim, path, path.head)) 
+}
 
 
+/*
 def first_tour_heuristics(dim: Int, path: Path): Option[Path] = {
   if (path.length == dim * dim) Some(path)
   else
-    first(ordered_moves(dim, path, path.head), (x: Pos) => first_tour_heuristics(dim, x::path))
+    for (p <- ordered_moves(dim, path, path.head))
+      val r = first_tour_heuristics(dim, x::path)
+    //first(ordered_moves(dim, path, path.head), (x: Pos) => first_tour_heuristics(dim, x::path))
+    ordered_moves(dim, path, path.head).view.flatMap((x: Pos) => first_tour_heuristics(dim, x::path)).headOption
 }
+*/ 
 
+/*
 for (dim <- 1 to 50) {
   val t = first_tour_heuristics(dim, List((dim / 2, dim / 2)))
   println(s"${dim} x ${dim}: " + (if (t == None) "" else { print_board(dim, t.get) ; "" }))
 }
+*/
+
+print_board(50, first_tour_heuristics(50, (25,25)::Nil).get)

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/slides/slides02.tex	Wed Nov 23 13:32:01 2016 +0000
@@ -0,0 +1,141 @@
+\documentclass[dvipsnames,14pt,t,xelatex]{beamer}
+\usepackage{../slides}
+\usepackage{../graphics}
+\usepackage{../langs}
+%\usepackage{../data}
+
+\hfuzz=220pt 
+
+%\setmonofont[Scale=.88]{Consolas}
+%\newfontfamily{\consolas}{Consolas}
+
+\lstset{language=Scala,
+        style=mystyle,
+        numbersep=0pt,
+        numbers=none,
+        xleftmargin=0mm}
+
+\newcommand{\bl}[1]{\textcolor{blue}{#1}}     
+
+% beamer stuff 
+\renewcommand{\slidecaption}{PEP (Scala) 02, King's College London}
+
+
+\begin{document}
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{%
+  \begin{tabular}{@ {}c@ {}}
+  \\[5mm]
+  \huge PEP Scala (2) 
+  \end{tabular}}
+
+  \normalsize
+  \begin{center}
+  \begin{tabular}{ll}
+  Email:  & christian.urban at kcl.ac.uk\\
+  Office: & S1.27 (1st floor Strand Building)\\
+  Slides \& Code: & KEATS
+  \end{tabular}
+  \end{center}
+
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     
+
+\begin{frame}[t]
+\frametitle{\begin{tabular}{c}Why Scala?\end{tabular}}
+
+
+\begin{itemize}
+\item \large {\bf You can avoid \textcolor{blue}{\texttt{null}}}:
+\end{itemize}
+
+
+\begin{textblock}{6}(1,5)
+  \begin{bubble}[10.5cm]\small
+      ``I call it my billion-dollar mistake. It was the invention of
+      the null reference in 1965. At that time, I was designing the
+      first comprehensive type system for references in an object
+      oriented language (ALGOL W). My goal was to ensure that all use
+      of references should be absolutely safe, with checking performed
+      automatically by the compiler. But I couldn't resist the
+      temptation to put in a null reference, simply because it was so
+      easy to implement. This has led to innumerable errors,
+      vulnerabilities, and system crashes, which have probably caused
+      a billion dollars of pain and damage in the last forty years.''
+      \hfill Sir Tony (Hoare)
+\end{bubble}
+\end{textblock}
+  
+\begin{textblock}{5}(11.8,1)
+\includegraphics[scale=0.20]{hoare.jpg}\\
+\end{textblock}
+  
+\end{frame}
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
+\frametitle{\huge\textbf{\texttt{return}}}
+
+\begin{center}\LARGE
+you should never use it
+\end{center}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
+\frametitle{Types}
+
+\begin{itemize}
+\item Base types\smallskip
+
+  \begin{tabular}{@{}l@{}}
+    \textcolor{codegreen}{\texttt{Int}},
+    \textcolor{codegreen}{\texttt{Long}},
+    \textcolor{codegreen}{\texttt{BigInt}},
+    \textcolor{codegreen}{\texttt{Float}},
+    \textcolor{codegreen}{\texttt{Double}}\\
+    \textcolor{codegreen}{\texttt{String}},
+    \textcolor{codegreen}{\texttt{Char}}\\
+    \textcolor{codegreen}{\texttt{Boolean}}
+  \end{tabular}
+
+\item Compound types \smallskip   
+
+  \begin{tabular}{@{}ll@{}}
+    \textcolor{codegreen}{\texttt{List[Int]}}     & lists of Int's \\
+    \textcolor{codegreen}{\texttt{Set[Double]}}   & sets of Double's \\
+    \textcolor{codegreen}{\texttt{(Int, String)}} & Int-String pair\\
+    \textcolor{codegreen}{\texttt{List[(BigInt, String)]}} &
+                                      lists of BigInt-String\\
+                                      & pairs\\
+    \textcolor{codegreen}{\texttt{List[List[Int]]}} & list of lists of Int's\\                                  
+  \end{tabular}
+
+\end{itemize}  
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
+\frametitle{\begin{tabular}{c}\\[3cm]\alert{Questions?}\end{tabular}}
+
+\mbox{}
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
+\end{document}
+
+
+\end{document}
+
+%%% Local Variables:  
+%%% mode: latex
+%%% TeX-master: t
+%%% End: 
+

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/slides/slides03.tex	Wed Nov 23 13:32:01 2016 +0000
@@ -0,0 +1,141 @@
+\documentclass[dvipsnames,14pt,t,xelatex]{beamer}
+\usepackage{../slides}
+\usepackage{../graphics}
+\usepackage{../langs}
+%\usepackage{../data}
+
+\hfuzz=220pt 
+
+%\setmonofont[Scale=.88]{Consolas}
+%\newfontfamily{\consolas}{Consolas}
+
+\lstset{language=Scala,
+        style=mystyle,
+        numbersep=0pt,
+        numbers=none,
+        xleftmargin=0mm}
+
+\newcommand{\bl}[1]{\textcolor{blue}{#1}}     
+
+% beamer stuff 
+\renewcommand{\slidecaption}{PEP (Scala) 02, King's College London}
+
+
+\begin{document}
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{%
+  \begin{tabular}{@ {}c@ {}}
+  \\[5mm]
+  \huge PEP Scala (2) 
+  \end{tabular}}
+
+  \normalsize
+  \begin{center}
+  \begin{tabular}{ll}
+  Email:  & christian.urban at kcl.ac.uk\\
+  Office: & S1.27 (1st floor Strand Building)\\
+  Slides \& Code: & KEATS
+  \end{tabular}
+  \end{center}
+
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     
+
+\begin{frame}[t]
+\frametitle{\begin{tabular}{c}Why Scala?\end{tabular}}
+
+
+\begin{itemize}
+\item \large {\bf You can avoid \textcolor{blue}{\texttt{null}}}:
+\end{itemize}
+
+
+\begin{textblock}{6}(1,5)
+  \begin{bubble}[10.5cm]\small
+      ``I call it my billion-dollar mistake. It was the invention of
+      the null reference in 1965. At that time, I was designing the
+      first comprehensive type system for references in an object
+      oriented language (ALGOL W). My goal was to ensure that all use
+      of references should be absolutely safe, with checking performed
+      automatically by the compiler. But I couldn't resist the
+      temptation to put in a null reference, simply because it was so
+      easy to implement. This has led to innumerable errors,
+      vulnerabilities, and system crashes, which have probably caused
+      a billion dollars of pain and damage in the last forty years.''
+      \hfill Sir Tony (Hoare)
+\end{bubble}
+\end{textblock}
+  
+\begin{textblock}{5}(11.8,1)
+\includegraphics[scale=0.20]{hoare.jpg}\\
+\end{textblock}
+  
+\end{frame}
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
+\frametitle{\huge\textbf{\texttt{return}}}
+
+\begin{center}\LARGE
+you should never use it
+\end{center}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
+\frametitle{Types}
+
+\begin{itemize}
+\item Base types\smallskip
+
+  \begin{tabular}{@{}l@{}}
+    \textcolor{codegreen}{\texttt{Int}},
+    \textcolor{codegreen}{\texttt{Long}},
+    \textcolor{codegreen}{\texttt{BigInt}},
+    \textcolor{codegreen}{\texttt{Float}},
+    \textcolor{codegreen}{\texttt{Double}}\\
+    \textcolor{codegreen}{\texttt{String}},
+    \textcolor{codegreen}{\texttt{Char}}\\
+    \textcolor{codegreen}{\texttt{Boolean}}
+  \end{tabular}
+
+\item Compound types \smallskip   
+
+  \begin{tabular}{@{}ll@{}}
+    \textcolor{codegreen}{\texttt{List[Int]}}     & lists of Int's \\
+    \textcolor{codegreen}{\texttt{Set[Double]}}   & sets of Double's \\
+    \textcolor{codegreen}{\texttt{(Int, String)}} & Int-String pair\\
+    \textcolor{codegreen}{\texttt{List[(BigInt, String)]}} &
+                                      lists of BigInt-String\\
+                                      & pairs\\
+    \textcolor{codegreen}{\texttt{List[List[Int]]}} & list of lists of Int's\\                                  
+  \end{tabular}
+
+\end{itemize}  
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
+\frametitle{\begin{tabular}{c}\\[3cm]\alert{Questions?}\end{tabular}}
+
+\mbox{}
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
+\end{document}
+
+
+\end{document}
+
+%%% Local Variables:  
+%%% mode: latex
+%%% TeX-master: t
+%%% End: 
+