Binary file pics/chess.jpg has changed
--- a/progs/lecture3.scala Mon Nov 21 15:57:45 2022 +0000
+++ b/progs/lecture3.scala Fri Nov 25 00:03:15 2022 +0000
@@ -1,6 +1,57 @@
// Scala Lecture 3
//=================
+// - maps (behind for-comprehensions)
+// - Pattern-Matching
+
+abstract class Rexp
+case object ZERO extends Rexp // matches nothing
+case object ONE extends Rexp // matches the empty string
+case class CHAR(c: Char) extends Rexp // matches a character c
+case class ALT(r1: Rexp, r2: Rexp) extends Rexp // alternative
+case class SEQ(r1: Rexp, r2: Rexp) extends Rexp // sequence
+case class STAR(r: Rexp) extends Rexp // star
+
+def depth(r: Rexp) : Int = r match {
+ case ZERO => 1
+ case ONE => 1
+ case CHAR(_) => 1
+ case ALT(r1, r2) => 1 + List(depth(r1), depth(r2)).max
+ case SEQ(r1, r2) => 1 + List(depth(r1), depth(r2)).max
+ case STAR(r1) => 1 + depth(r1)
+}
+
+
+// - String-Interpolations
+
+// String Interpolations
+//=======================
+
+def cube(n: Int) : Int = n * n * n
+
+val n = 3
+println("The cube of " + n + " is " + cube(n) + ".")
+
+println(s"The cube of $n is ${cube(n)}.")
+
+// or even
+
+println(s"The cube of $n is ${n * n * n}.")
+
+// helpful for debugging purposes
+//
+// "The most effective debugging tool is still careful
+// thought, coupled with judiciously placed print
+// statements."
+// — Brian W. Kernighan, in Unix for Beginners (1979)
+
+
+def gcd_db(a: Int, b: Int) : Int = {
+ println(s"Function called with $a and $b.")
+ if (b == 0) a else gcd_db(b, a % b)
+}
+
+gcd_db(48, 18)
// naive quicksort with "On" function
Binary file slides/slides03.pdf has changed
--- a/slides/slides03.tex Mon Nov 21 15:57:45 2022 +0000
+++ b/slides/slides03.tex Fri Nov 25 00:03:15 2022 +0000
@@ -1,8 +1,8 @@
% !TEX program = xelatex
\documentclass[dvipsnames,14pt,t,xelatex,aspectratio=169,xcolor={table}]{beamer}
-\usepackage{../slides}
-\usepackage{../graphics}
-\usepackage{../langs}
+\usepackage{../styles/slides}
+\usepackage{../styles/mygraphs}
+\usepackage{../styles/langs}
%%\usepackage{../data}
\usetikzlibrary{shapes}
\usepackage[export]{adjustbox}
@@ -54,9 +54,11 @@
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\\
- \multicolumn{2}{c}{\Large\textbf{https://pollev.com/cfltutoratki576}}\\
+
+ Office Hour: & Fridays 11:00 -- 12:00\\
+ Location: & N7.07 (North Wing, Bush House)\bigskip\\
+
+ Pollev: & \texttt{\alert{https://pollev.com/cfltutoratki576}}\\ \\
\end{tabular}
\end{center}
@@ -119,7 +121,7 @@
collatzHelper(n) // a = 0
\end{lstlisting}
-\DOWNarrow{1}{10.7}{3.4}
+\DOWNarrow{1}{8.3}{3.4}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@@ -356,41 +358,41 @@
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\begin{frame}[t]
-\frametitle{Preliminary 1 (Scala)}
-
-Raw marks (298 submissions):\bigskip
-
-\begin{itemize}
-\item 3\%: \hspace{4mm}227
-\item 2\%: \hspace{4mm}35
-\item 1\%: \hspace{4mm}9
-\item 0\%: \hspace{4mm}27
-\end{itemize}
-
-
-\end{frame}
+%\begin{frame}[t]
+%\frametitle{Preliminary 1 (Scala)}
+%
+%Raw marks (298 submissions):\bigskip
+%
+%\begin{itemize}
+%\item 3\%: \hspace{4mm}227
+%\item 2\%: \hspace{4mm}35
+%\item 1\%: \hspace{4mm}9
+%\item 0\%: \hspace{4mm}27
+%\end{itemize}
+%
+%
+%\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\begin{frame}[t]
-\frametitle{Preliminary 2 (Scala)}
-
-Raw marks (301 submissions):\bigskip
-
-\begin{itemize}
-\item 3.0\%: \hspace{4mm}236
-\item 2.5\%: \hspace{4mm}5
-\item 2.0\%: \hspace{4mm}7
-\item 1.5\%: \hspace{4mm}13
-\item 1.0\%: \hspace{4mm}1
-\item 0.5\%: \hspace{4mm}2
-\item 0.0\%: \hspace{4mm}37
-\end{itemize}
-
-
-\end{frame}
-
-\begin{frame}<1-20>
-\end{frame}
+%\begin{frame}[t]
+%\frametitle{Preliminary 2 (Scala)}
+%
+%Raw marks (301 submissions):\bigskip%
+%
+%\begin{itemize}
+%\item 3.0\%: \hspace{4mm}236
+%\item 2.5\%: \hspace{4mm}5
+%\item 2.0\%: \hspace{4mm}7
+%\item 1.5\%: \hspace{4mm}13
+%\item 1.0\%: \hspace{4mm}1
+%\item 0.5\%: \hspace{4mm}2
+%\item 0.0\%: \hspace{4mm}37
+%\end{itemize}
+%
+%
+%\end{frame}
+%
+%\begin{frame}<1-20>
+%\end{frame}
\end{document}
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/wsheets/wsh03.tex Fri Nov 25 00:03:15 2022 +0000
@@ -0,0 +1,190 @@
+% !TEX program = xelatex
+\documentclass{article}
+\usepackage{../styles/style}
+\usepackage{../styles/langs}
+\usepackage{tikz}
+\usepackage{pgf}
+\usepackage{marvosym}
+\usepackage{boxedminipage}
+
+\lstset{escapeinside={/*!}{!*/}}
+\newcommand{\annotation}[1]{\hfill\footnotesize{}#1}
+
+\usepackage{menukeys}
+
+
+% Exact colors from NB
+\usepackage[breakable]{tcolorbox}
+\definecolor{incolor}{HTML}{303F9F}
+\definecolor{outcolor}{HTML}{D84315}
+\definecolor{cellborder}{HTML}{CFCFCF}
+\definecolor{cellbackground}{HTML}{F7F7F7}
+
+
+
+\begin{document}
+\fnote{\copyright{} Christian Urban, King's College London, 2022}
+
+\section*{Scala Worksheet 3}
+
+
+
+\subsection*{Task 1 (Options)}
+
+Get familiar with the return value of functions that can
+``go wrong'':
+
+\begin{lstlisting}[numbers=none]
+scala> List(7,2,3,4,5,6).find(_ < 4)
+scala> List(5,6,7,8,9).find(_ < 4)
+scala> List(5,6,7,8,9).min
+scala> List(5,6,7,8,9).minOption
+scala> List[Int]().minOption
+\end{lstlisting}
+
+\noindent
+Note that there needs to be a type-annotation for \texttt{List()} otherwise
+Scala will not know which \texttt{min}-version it should use.
+
+\subsection*{Task 2 (Try)}
+
+The Scala-Idiom \texttt{Try-getOrElse} allows you to conveniently
+deal with failure cases.
+
+\begin{lstlisting}[numbers=none]
+scala> Try(Some(List(5,6,7,8,9).min)).getOrElse(None)
+scala> Try(Some(List[Int]().min)).getOrElse(None)
+\end{lstlisting}
+
+\noindent
+Note that \texttt{Try} needs the library \texttt{scala.util.\_} to be
+imported.
+
+
+\begin{lstlisting}[numbers=none]
+def safe_div(x: Int, y: Int) : Option[Int] =
+ Try(Some(x / y)).getOrElse(None)
+\end{lstlisting}
+
+\subsection*{Task 3 (URLs / Files)}
+
+For simple tasks such as reading webpages and files, Scala provides
+convenient functions \texttt{Source.fromURL} and \texttt{Source.fromFile}.
+To try them out, you need to import \texttt{io.Source}.
+
+\begin{lstlisting}[numbers=none]
+scala> Source.fromURL(my_url)("ISO-8859-1").mkString
+scala> Source.fromFile(my_file)("ISO-8859-1").mkString
+\end{lstlisting}
+
+\noindent
+These functions return an iterator, which can be transformed into a String
+using \texttt{mkString}. The second argument fixes the character encoding
+and should not be omitted. If you are interested in the individual lines
+in the file, for example, you can use
+
+\begin{lstlisting}[numbers=none]
+Source.fromFile(my_file)("ISO-8859-1")
+ .getLines().toList
+\end{lstlisting}
+
+\noindent
+If you are after proper error-handling, then you can use Scala's options
+as follows
+
+\begin{lstlisting}[numbers=none]
+Try(Some(Source.fromFile("test.txt")("ISO-8859-1")
+ .mkString)).getOrElse(None)
+\end{lstlisting}
+
+This can also be written slightly shorter as
+
+\begin{lstlisting}[numbers=none]
+Try(Source.fromFile("test.txt")("ISO-8859-1")
+ .mkString).toOption
+\end{lstlisting}
+
+\noindent
+In case of reading files, there can be an issue with closing
+files properly. For this Scala provides \texttt{Using}
+
+\begin{lstlisting}[numbers=none]
+ Using(Source.fromFile("test.txt")("ISO-8859-1"))
+ (_.mkString).toOption
+\end{lstlisting}
+
+\noindent
+This closes the files automatically after reading, but otherwise
+behaves as the code shown above: It gives a \texttt{Some} in the
+success case and \texttt{None} in the failure case. However,
+\texttt{Using} requires a function as argument for prescribing
+of what to do with the file content in the success case.
+
+\subsection*{Task 4 (Higher-Order Functions)}
+
+Higher-Order functions means that Scala allows functions to
+have functions as arguments and also allows functions to
+return functions. Get familiar with the short-hand notation
+for simple functions
+
+\begin{lstlisting}[numbers=none]
+scala> List(7,2,3,4,5,6).find(_ < 4)
+scala> List(7,2,3,4,5,6).count(_ % 2 == 0)
+scala> List(7,2,3,4,5,6).sortWith(_ > _)
+scala> List(7,2,3,4,5,6).filter(_ > 4)
+\end{lstlisting}
+
+\noindent
+Be aware that this short-hand notation only works for ``smallish'' functions
+and that sometimes Scala cannot figure out the types involved without
+explicit type annotations.
+
+\subsection*{Task 5 (Maps)}
+
+Get familiar with the map-function for lists, sets etc. It is the
+quintessential higher-order function and frequently used for transforming
+lists.
+
+\begin{lstlisting}[numbers=none]
+scala> List(7,2,3,4,5,6).map(n => n * n)
+\end{lstlisting}
+
+\noindent
+Make also sure you see that Scala's \texttt{for}-comprehensions
+are just syntactic sugar for \texttt{map}s. What would this
+expression look like as \texttt{for}-comprehension? What are
+the advantages of \texttt{for}-comprehensions over \texttt{map}s.
+
+
+\subsection*{Task 6 (Pattern-Matching)}
+
+Rewrite the following function using pattern-matching
+
+\begin{lstlisting}[numbers=none]
+def my_map(lst: List[Int], f: Int => Int) : List[Int] = {
+ if (lst == Nil) Nil
+ else f(lst.head) :: my_map(lst.tail, f)
+}
+\end{lstlisting}
+
+\noindent
+Observe that the type of the function is from \texttt{Int}s to
+\texttt{Int}s, which is written in Scala as type \texttt{Int => Int}.
+
+
+\subsection*{Task 7 (Fold, Hard)}
+
+Implement a function \texttt{fold} for lists of integers. It takes
+a list of integers as argument as well as a function $f$ and a unit element $u$.
+The function is of type \texttt{(Int, Int) => Int} and the unit element
+is an integer. The return type of \texttt{fold} is \texttt{Int}.
+What is \texttt{fold} supposed to do? Well it should fold the function $f$
+over the elements of the list and in case of the empty list return the
+unit element $u$.
+
+\end{document}
+
+%%% Local Variables:
+%%% mode: latex
+%%% TeX-master: t
+%%% End: 
