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\begin{document}

\fnote{\copyright{} Christian Urban, King's College London, 2022}

\section*{Scala Worksheet 1}

Please install Scala on your work-machine: You should have

Scala up and running after this week, and also have an IDE that allows you to

access the Scala REPL. Some installation instructions are given at

\begin{center}

\url{https://www.scala-lang.org/download/2.13.10.html}

\end{center}  

\subsubsection*{MacOSX}

\begin{itemize}

\item[0)] (if needed) \texttt{brew install java} \;\;or\;\; \texttt{brew reinstall java}

\item[1)] \texttt{brew install scala@2.13}

\end{itemize}

\noindent Another method to install Scala on MacOSX

\begin{itemize} 

\item[1)] \texttt{curl -s "https://get.sdkman.io" | bash}

\item[2)] \texttt{sdk install scala 2.13.10}  

\end{itemize}

\subsubsection*{Windows / Linux Ubuntu}

\begin{itemize}

\item[0)] (if needed) \texttt{sudo apt-get remove scala-library scala}

\item[1)] {\fontsize{8.5}{8.5}\selectfont\texttt{sudo wget https://downloads.lightbend.com/scala/2.13.10/scala-2.13.10.deb}}

\item[2)] \texttt{sudo dpkg -i scala-2.13.10.deb}  

\end{itemize}

\noindent

Other Linux distros: \texttt{sudo apt-get scala}\bigskip

\noindent In the end you should have something running like in your terminal/shell:

\begin{lstlisting}[language={},numbers=none,basicstyle=\ttfamily\small]

$ scala

Welcome to Scala 2.13.10 (OpenJDK 64-Bit Server VM, Java 17.0.1).

Type in expressions for evaluation. Or try :help.

scala>

\end{lstlisting}%$

\noindent

If you want to use VS Code or Codium, you might want to also look into setting up

a key-shortcut for ``Run‐Selected‐Text‐In‐Active‐Terminal'' and also set up

syntax highlighting. Have a look at the Scala handout uploaded to KEATS for information.\bigskip

\noindent

Make sure you have checked out the template files for the Scala CWs and registered the

Github repository on KEATS. See whether you receive a test report when pushing some code.

\newpage

\subsection*{Task 1}

`Play' with the Scala REPL and try out the following queries. Observe

what Scala responds. Does it make sense?

\begin{lstlisting}[numbers=none]

scala> 2 + 2

scala> 1 / 2

scala> 1.0 / 2

scala> 1 / 2.0

scala> 1 / 0

scala> 1.0 / 0.0

scala> true == false

scala> true && false

scala> 1 > 1.0

scala> "12345".length

scala> List(1,2,1).size

scala> Set(1,2,1).size

scala> List(1) == List(1)

scala> Set(1,2,3) == Set(3,2,1)

scala> Array(1) == Array(1)

scala> Array(1).sameElements(Array(1))

\end{lstlisting}

\subsection*{Task 2 (Vals)}

Type in the value declarations below and observe Scala's responses. Explain what

is printed as the value for \texttt{x} in the last line. Is \texttt{z} re-assigned

in the 4th line?

\begin{lstlisting}[numbers=none]

scala> val z = 42

scala> z = z + 1

scala> val x = 2 * z

scala> val z = 466

scala> println(x)

\end{lstlisting}

\subsection*{Task 3 (Strings)}

Get familiar with constructing strings and printing strings

(i.e.~\texttt{println}, \texttt{mkString}, \texttt{toString}, \ldots)

\begin{lstlisting}[numbers=none]

scala> println("Hello " ++ "World")

scala> List(1,2,3,4).mkString("\n")

scala> List(1,2,3,4).mkString("(", "|", ")")

\end{lstlisting}

\subsection*{Task 4 (Functions)}

Write a function \texttt{miles2meters} taking an integer as argument

and generating an integer. You can assume that one mile is 1609 meters.

Remember that functions in Scala do not use the \texttt{return}-keyword.

\subsection*{Task 5 (If-Conditions)}

Make sure you understand if-conditions in Scala: They are

\emph{expressions}, meaning they need to calculate a result. For

example an \texttt{if} without an else-branch is nearly always

\emph{not} what you intend to write (because you are not meant to

change any ``state'' outside the expression). Also, remember the quirks

in Scala with if-conditions needing parentheses and there is no

\texttt{then}-keyword.

\begin{lstlisting}[numbers=none]

scala> val s1 = "foo"

scala> val s2 = "bar"

scala  val s3 = "foobar"

scala> if (s1 == s2) print("equal") else print("unequal")

scala> if (s1 ++ s2 == s3) print("equal") else print("unequal")

\end{lstlisting}

\subsection*{Task 6 (For-Comprehensions, Harder)}

Write \texttt{for}-comprehensions that enumerate all triples containing the numbers 1 - 5. That is,

print the list

\[

\texttt{(1,1,1)}, \texttt{(2,1,1)}, \texttt{(3,1,1)} \;\ldots\; \texttt{(5,5,5)}

\]

\noindent

Modify the \texttt{for}-comprehensions such that only triples are

printed where the sum is divisible by 3.  Then sort the list according

to the middle element (for this use \texttt{sortBy}).

\subsection*{Task 7 (Recursion, Advanced /Hard)}

Write a pretty print function for lists of integers which

``condenses'' elements in the list, meaning if there is a number

several times in a row, then print out \mbox{\texttt{n x e}}, where

\texttt{n} is the number of repetitions and \texttt{e} is the

number. For example

\begin{lstlisting}[numbers=none]

  List(1,1,1,2,3,3)    =>   List(3 x 1, 2, 2 x 3)

  List(1,2,3,4,4,4)    =>   List(1, 2, 3, 3 x 4)

  List(1,1,1,1,1,1)    =>   List(6 x 1)

  List(1,1,1,2,1,1)    =>   List(3 x 1, 2, 2 x 1)

\end{lstlisting}

You might like to define a separate function that first counts the occurences

for each element and returns a list of (Int, Int)-pairs .

\end{document}

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