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\renewcommand{\slidecaption}{PEP (Scala) 02, King's College London}

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\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: & N\liningnums{7.07} (North Wing, Bush House)\bigskip\\

    Slides \& Code: & KEATS\bigskip\\

    Office Hours: &  Thursdays 12:00 -- 14:00\\

    Additionally: & (for Scala) Tuesdays 10:45 -- 11:45\\ 

  \end{tabular}

  \end{center}

\end{frame}

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\begin{frame}[c,fragile]

  \frametitle{Scala 2.13.1}

  \begin{lstlisting}[language={},numbers=none,

    basicstyle=\ttfamily\small,xleftmargin=-2mm]

  $ scala

  Welcome to Scala 2.13.1 (Java HotSpot(TM) 

  64-Bit Server VM, Java 9). Type in expressions 

  for evaluation. Or try :help.

  scala>

  \end{lstlisting}%$

  \bigskip\bigskip

  With older versions you will get strange results with my reference implementation.

  \end{frame}

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\begin{frame}[c,fragile]

\frametitle{Reference Implementation}

Keep your implementation and my reference implementation separate.\bigskip

  \begin{lstlisting}[language={},numbers=none,

    basicstyle=\ttfamily\small,xleftmargin=-2mm]

  $ scala -cp collatz.jar

  scala> CW6a.collatz(6)

  res0: Long = 8

  scala> import CW6a._

  scala> collatz(9)

  res1: Long = 19

  \end{lstlisting}%$

\end{frame}

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\begin{frame}[t]

  \frametitle{Preliminary Part 7}

  \Large

  \[

    \texttt{overlap}(d_1, d_2) = \frac{d_1 \cdot d_2}{max(d_1^2, d_2^2)}  

  \]\bigskip

  \large

  \quad{}\;where \;$d_1^2$\; means \;$d_1 \cdot d_1$\; and so on

\end{frame}

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\begin{frame}[c]

  \frametitle{Discussion Forum}

  \large

  ``Since we can't use \code{var}s I was wondering if we could use a stack?''

  \bigskip\bigskip\bigskip\bigskip

  \small

  My \pcode{collatz} and \pcode{collatz_max} functions are 4 loc each. 

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\begin{frame}[t]

  \frametitle{Email: Hate 'val'}

  \mbox{}\\[-22mm]\mbox{}

  \begin{center}

    \begin{bubble}[10.5cm]

    Subject: \textbf{Hate '\textbf{\texttt{val}}'}\hfill 01:00 AM\medskip\\

    Hello Mr Urban,\medskip\\

    I just wanted to ask, how are we suppose to work

    with the completely useless \textbf{\texttt{val}}, that can’t be changed ever? Why is

    this rule active at all? I’ve spent 4 hours not thinking on the

    coursework, but how to bypass this annoying rule. What’s the whole

    point of all these coursework, when we can’t use everything Scala

    gives us?!?\medskip\\

    Regards.\\

    \mbox{}\hspace{5mm}\textcolor{black!50}{<<deleted>>}\\

    \end{bubble}

  \end{center}

\end{frame}

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\begin{frame}[c]

 \mbox{}\\[-25mm]\mbox{}

\begin{center}

  \begin{bubble}[10.5cm]

  Subject: \textbf{Re: Hate '\textbf{\texttt{val}}'}\hfill 01:02 AM\bigskip\bigskip\\

  \textcolor{black!70}{

    \textit{\large<<my usual rant about fp\ldots\\ concurrency bla bla\ldots{} better programs

    yada>>}}\bigskip\bigskip\bigskip

  PS: What are you trying to do where you desperately want to use \texttt{var}?

  \end{bubble}

\end{center}

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\begin{frame}[c,fragile]

\begin{textblock}{6}(0.5,0.5)

\begin{bubble}[11.5cm]

  \small  

  Subject: \textbf{Re: Re: Hate '\textbf{\texttt{val}}'}\hfill 01:04 AM\medskip\\

  \textbf{Right now my is\_legal function works fine:}

\footnotesize\begin{lstlisting}[language=Scala, numbers=none, xleftmargin=-1mm]

 def is_legal(dim: Int, path: Path)(x: Pos): Boolean = {

   var boolReturn = false

   if(x._1 > dim || x._2 > dim || x._1 < 0 || x._2 < 0) {

   else { var breakLoop = false

          if(path == Nil) { boolReturn = true }

          else { for(i <- 0 until path.length) {

                    if(breakLoop == false) {

                      if(path(i) == x) {

                        boolReturn = true

                        breakLoop = true

                      }

                      else { boolReturn = false }

                    } else breakLoop

            }

          }

          boolReturn

   }

\end{lstlisting}

\end{bubble}

\end{textblock}

\begin{textblock}{6}(8.2,11.8)

\begin{bubble}[5.5cm]\footnotesize\bf

\ldots{}but I can’t make it work with boolReturn being val. What approach would

you recommend in this case, and is using var in this case justified?

\end{bubble}

\end{textblock}

\only<2>{

\begin{textblock}{6}(0.3,11.8)

  \begin{bubble}[3.1cm]

    \textbf{Me:}

    \raisebox{-12mm}{\includegraphics[scale=0.08]{../pics/throwup.jpg}}

  \end{bubble}

\end{textblock}}

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\mbox{}\\[-25mm]\mbox{}

\begin{textblock}{6}(0.5,2)

  \begin{bubble}[11.5cm]

  Subject: \textbf{Re: Re: Re: Hate '\textbf{\texttt{val}}'}\hfill 01:06 AM\bigskip\\

  \small

  OK. So you want to make sure that the \texttt{x}-position is not outside the

  board....and furthermore you want to make sure that the \texttt{x}-position

  is not yet in the path list. How about something like\bigskip

\footnotesize\begin{lstlisting}[language=Scala, numbers=none, xleftmargin=-1mm]

 def is_legal(dim: Int, path: Path)(x: Pos): Boolean = 

   ...<<some board conditions>>... && !path.contains(x)

\end{lstlisting}\bigskip

  \small Does not even contain a \texttt{val}.

  \end{bubble}

\end{textblock}

\begin{textblock}{6}(7,12)

\footnotesize\textcolor{black!50}{(This is all on one line)}

\end{textblock}

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\begin{frame}[t,fragile]

\mbox{}\\[-15mm]\mbox{}

\begin{textblock}{6}(1,3)

  \begin{bubble}[10.5cm]

    Subject: \textbf{Re: Re: Re: Re: Hate '\textbf{\texttt{val}}'}\hfill 11:02 AM\bigskip\bigskip\\

    THANK YOU! You made me change my coding perspective. Because of you,

    I figured out the next one\ldots

  \end{bubble}

\end{textblock}

\only<2>{

\begin{textblock}{6}(0.3,11.8)

  \begin{bubble}[3.1cm]

    \textbf{Me:}

    \raisebox{-12mm}{\includegraphics[scale=0.15]{../pics/happy.jpg}}

  \end{bubble}

\end{textblock}}

\end{frame}

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\begin{frame}[c]

\frametitle{Assignments}

Don't change any names or types in the templates!\bigskip

Avoid at all costs:

\begin{itemize}

\item \code{var} 

\item \code{return} 

\item \texttt{ListBuffer}

\item \texttt{mutable}

\item \texttt{.par}  

\end{itemize}\bigskip\bigskip

I cannot think of a good reason to use stacks.

\end{frame}

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\begin{frame}[t]

\frametitle{For-Comprehensions Again}

\begin{center}

  \begin{tikzpicture}[scale=1,

                      node/.style={

                      rectangle,rounded corners=3mm,

                      very thick,draw=black!50,

                      minimum height=18mm, minimum width=20mm,

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  \node (A0) at (0.1,0) {\texttt{\textcolor{purple}{\textbf{for}} (\alert<2->{n} <- List(}};

  \node (A1) at (2.3,0) {\texttt{\phantom{,}1,}};

  \node (A2) at (3.2,0) {\texttt{\phantom{,}2,}};

  \node (A3) at (4.1,0) {\texttt{\phantom{,}3,}};

  \node (A4) at (5.0,0) {\texttt{\phantom{,}4,}};

  \node (A5) at (5.9,0) {\texttt{\phantom{))}5))}};

  \node (A6) at (8,0) {\texttt{\textcolor{purple}{\textbf{yield}} \alert<2->{n\,*\,n}}};

  \onslide<2->{

  \node (B0) at (1.4,-3) {\texttt{List(}};

  \node (B1) at (2.3,-3) {\texttt{\phantom{,}1,}};

  \node (B2) at (3.6,-3) {\texttt{\phantom{,}4,}};

  \node (B3) at (4.9,-3) {\texttt{\phantom{,}9,}};

  \node (B4) at (6.2,-3) {\texttt{\phantom{,}16,}};

  \node (B5) at (7.5,-3) {\texttt{\phantom{,}25)}};}

  \onslide<2->{

  \draw [->,line width=1mm] (A1.south) -- (B1.north);

  \draw [->,line width=1mm] (A2.south) -- (B2.north);

  \draw [->,line width=1mm] (A3.south) -- (B3.north);

  \draw [->,line width=1mm] (A4.south) -- (B4.north);

  \draw [->,line width=1mm] (A5.south) -- (B5.north);}

  \onslide<2->{

  \node (Q1) at (-0.45,-0.1) {};

  \node (Q2) at (-0.45,-2.8) {};

  \node (Q3) at (-0.45,-2.95) {\alert<2->{\texttt{n\,*\,n:}}};

  \draw [->,red,line width=1mm] (Q1.south) -- (Q2.north);}

 \end{tikzpicture}

\end{center}

\onslide<3>{This is for when the for-comprehension\\ \textbf{yields / produces} a result.}

\end{frame}

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\begin{frame}[t]

\frametitle{For-Comprehensions Again}

\begin{center}

  \begin{tikzpicture}[scale=1,

                      node/.style={

                      rectangle,rounded corners=3mm,

                      very thick,draw=black!50,

                      minimum height=18mm, minimum width=20mm,

                      top color=white,bottom color=black!20}]

  \node (A0) at (0,0)

    {\texttt{\textcolor{purple}{\textbf{for}} (n <- List(1, 2, 3, 4, 5))

             \textcolor{purple}{\textbf{yield}} n\,*\,n}};

  \node (A1) at (0,-1.5) {\LARGE\textbf{vs}};       

  \node (A2) at (0,-3)

    {\texttt{\textcolor{purple}{\textbf{for}} (n <- List(1, 2, 3, 4, 5)) println(n)}};

 \end{tikzpicture}

\end{center}\bigskip

The second version is in case the for \textbf{does not}

produce any result.

\end{frame}

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\begin{frame}[c,fragile]

  %\frametitle{Option Type}

  Find something below 4 in a list. What do you think Scala answers?\bigskip\bigskip

  \begin{onlyenv}<1>

  \begin{lstlisting}[language=Scala, numbers=none, xleftmargin=-1mm]

  List(7,2,3,4,5,6).find(_ < 4)

  List(5,6,7,8,9).find(_ < 4)

  \end{lstlisting}

  \end{onlyenv}

  \begin{onlyenv}<2>

  \begin{lstlisting}[language=Scala, numbers=none, xleftmargin=-1mm]

  List(7,2,3,4,5,6).find(_ < 4)

  res: Option[Int] = Some(2)

  List(5,6,7,8,9).find(_ < 4)

  res: Option[Int] = None

  \end{lstlisting}

  \end{onlyenv}

  \end{frame}

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\begin{frame}[c]

\frametitle{Option Type}

\begin{itemize}

\item if the value is present, you use\bigskip

\begin{center}\pcode{Some(value)}\end{center}\bigskip\bigskip

\item if no value is present, you use\bigskip

\begin{center}\pcode{None}\end{center}\bigskip\bigskip

\end{itemize}

\small e.g.~\code{Option[Int]}, then \code{Some(42)} and \code{None}\\

good for error handling      

\end{frame}

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\begin{frame}[c,fragile]

\frametitle{Option Type}

\small   

\begin{onlyenv}<1>

\begin{lstlisting}[language=Scala, numbers=none, xleftmargin=-1mm]

Integer.parseInt("1234")

// vs.

def get_me_an_int(s: String) : Option[Int] = 

 Try(Some(Integer.parseInt(s))).getOrElse(None)

\end{lstlisting}

\end{onlyenv}\bigskip\bigskip\bigskip

in the Scala code it is clear from the type I that have to deal 

with the \pcode{None}-case; no JavaDoc needed

\end{frame}

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\begin{frame}[c,fragile]

\frametitle{Higher-Order Functions}

In Scala, functions can take other functions as arguments and can return 

a function as a result.\bigskip\bigskip  

\begin{lstlisting}[language=Scala, numbers=none, xleftmargin=1mm]

List(7,2,3,4,5,6).find(_ < 4)

\end{lstlisting}

\UParrow{1}{10}{11}    

\end{frame}

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\begin{frame}[c,fragile]

\frametitle{Higher-Order Functions (2)}

\begin{lstlisting}[language=Scala, numbers=none, xleftmargin=1mm]

def even(x: Int) : Boolean = x % 2 == 0

List(1, 2, 3, 4, 5).filter(even)

  res : List[Int] = List(2, 4)

List(1, 2, 3, 4, 5).count(even)

  res : Int = 2

List(1, 2, 3, 4, 5).find(even)

  res: Option[Int] = Some(2)

\end{lstlisting}

\end{frame}

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\begin{frame}[c,fragile]

\frametitle{map (lower case)}

 applies a function to each element of a list (and more)

\begin{center}

\begin{tikzpicture}[scale=0.9]