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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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