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%cheat sheet+
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%http://worldline.github.io/scala-cheatsheet/+
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\begin{document}+
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\fnote{\copyright{} Christian Urban, King's College London, 2020, 2021, 2023}+
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+
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\section*{Scala 3 in 6CCS3CFL}+
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+
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For the coursework in this module you are free to use any programming+
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language you like, but I will show you all my code using Scala---I+
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hope you have fond memories of Scala from PEP. The only difference+
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with PEP is that I will the Ammonite REPL for Scala 3.+
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+
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\begin{tcolorbox}[colback=red!5!white,colframe=red!75!black]+
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If you intend to submit your code for the CW in Scala, you \underline{MUST} submit code that+
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is compatible with Scala 3!! This is to make it easier for me to test+
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your code and the changes between Scala 2 from last year PEP to Scala+
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3 in CFL are not that great. In fact, most changes are just some new+
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syntax.+
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\end{tcolorbox}\medskip+
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+
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\noindent+
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If you need a reminder of the Scala handouts from PEP updated to Scala 3+
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have a look here+
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\hr{http://talisker.nms.kcl.ac.uk/cgi-bin/repos.cgi/pep-material/raw-file/tip/handouts/pep-ho.pdf}. But as said, you do not need to use Scala for the CWs.\footnote{Haskell, Rust, Ocaml were other languages that have+
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  been used previously in CFL. I do not recommend to use Java or C or C++ for+
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  writing a compiler, but if you insist, feel free. It has been done+
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  before.}  +
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\bigskip+
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+
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\noindent+
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The other difference between the Scala I showed you in PEP is that in CFL+
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I will use the Ammonite REPL (with underlying Scala Version 3):+
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+
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\begin{quote}+
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\url{https://ammonite.io/#Ammonite-REPL}+
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\end{quote}+
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+
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\noindent+
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This is a drop-in replacement for the original Scala REPL and+
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works very similarly, for example+
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+
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\begin{lstlisting}[language={},numbers=none,basicstyle=\ttfamily\small]+
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$ amm+
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Loading...+
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Welcome to the Ammonite Repl 3.0.0-M2 (Scala 3.3.3 Java 21.0.4)+
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@ 1 + 2+
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res0: Int = 3+
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\end{lstlisting} %% $+
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+
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%%\runExtCmd[redirect]{ls -la}{voss}+
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+
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+
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\noindent+
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Ammonite uses the same Scala compiler, just adds some useful features+
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on top of it. It is quite main-stream in the Scala community and it should+
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therefore be very easy for you to install \texttt{amm}. If you work under+
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a Unix-like system, a sure way to install the right version of Ammonite+
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is by using \texttt{curl}:+
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+
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\begin{lstlisting}[numbers=none,language={},basicstyle=\ttfamily\small]+
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$ curl -L https://github.com/com-lihaoyi/Ammonite/releases/\+
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  download/3.0.0-M2/3.3-3.0.0-M2 --output amm+
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\end{lstlisting} %% $  +
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+
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\noindent+
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This creates a file \code{amm} which before it can be run might+
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need some adjustments of the permissions. Under recent versions of+
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Windows also have \texttt{curl}, but need a slightly different call:+
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+
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\begin{lstlisting}[numbers=none,language={},basicstyle=\ttfamily\small]+
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$ curl -L https://github.com/com-lihaoyi/Ammonite/releases/\+
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  download/3.0.0-M2/3.3-3.0.0-M2 --output amm.bat+
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\end{lstlisting} %% $  +
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+
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\noindent+
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Then you need to run Ammonite with \texttt{.$\backslash$amm} and there+
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is no need to change any permissions under Windows.  +
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+
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The big advantage of Ammonite is that it comes with some additional+
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libraries already built-in and also allows one to easily break up code+
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into smaller modules. For example reading and writing files in+
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Ammonite can be achieved with+
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+
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\begin{lstlisting}[numbers=none,language=Scala]+
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scala> import os._+
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scala> write.over(pwd / "file.name", "foo bar")  +
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scala> read(pwd / "file.name")   +
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res1: String = "foo bar"+
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\end{lstlisting}+
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+
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\noindent+
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The second line writes the string \code{"foo bar"} into the file+
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\code{"file.name"}, which is located in the current working+
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directory (\code{pwd}). For loading and accessing code from+
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another Scala file, you can import the code into Ammonite+
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as follows:+
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+
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\begin{lstlisting}[numbers=none,language=Scala]+
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import $file.name-of-the-file+
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import name-of-the-file._+
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\end{lstlisting}  %% $+
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+
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\noindent+
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This assumes the other Scala file is called+
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\texttt{name-of-the-file.sc} and requires the file to be in the same+
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directory where \texttt{amm} is working in. This will be very convenient +
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for the compiler we implement in CFL, because it allows us to easily+
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break up the code into the lexer, parser and code generator.+
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+
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Another handy feature of Ammonite is that you can mark functions as+
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\texttt{@main}. For example+
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+
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\begin{lstlisting}[numbers=none,language=Scala]+
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@main+
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def foo() = ...+
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\end{lstlisting}+
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+
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\noindent+
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This means you can now call that function from the command line like+
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+
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\begin{lstlisting}[numbers=none,language=Scala]+
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$ amm file.sc foo+
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\end{lstlisting} %% $+
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+
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\noindent+
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If you want to specify an argument on the commandline, say an int and+
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a string, then you can write+
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+
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\begin{lstlisting}[numbers=none,language=Scala]+
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@main+
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def bar(i: Int, s: String) = ...+
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\end{lstlisting}+
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+
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\noindent+
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and then call+
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+
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\begin{lstlisting}[numbers=none,language=Scala]+
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$ amm file.sc 42 foobar+
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\end{lstlisting} %% $+
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+
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\noindent+
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What is also good in Ammonite is that you can specify more than one+
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function to be ``main'' and then specify on the command line which+
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function you want to run as entry-point.+
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+
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Another feature you might like to use is that Ammonite can ``watch'' files.+
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This means it can automatically re-run a file when it is saved. For this+
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you have to call \texttt{amm} with the option \texttt{-w}, as in+
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+
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\begin{lstlisting}[numbers=none,language=Scala]+
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$ amm -w file.sc+
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\end{lstlisting} %% $+
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+
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\noindent Of course this requires that you use \texttt{println} for+
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inspecting any data as otherwise nothing will be displayed at the+
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commandline.+
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\smallskip+
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+
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\noindent+
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To sum up, Ammonite is a really useful addition to the Scala ecosystem.+
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You can find more information about how to use it in the first five chapters+
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of the ``Hands-on Scala'' book by Li Haoyi. These chapters are+
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free and can be used as a reference, see+
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+
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\begin{center}+
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\url{https://www.handsonscala.com/part-i-introduction-to-scala.html}+
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\end{center}+
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+
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\end{document}+
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