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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}+
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\section*{Scala 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. But as said, you do not+
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need to use Scala for your own code.\footnote{Haskell, Rust, Ocaml+
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  were other languages that have been used previously in CFL. I+
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  recommend to not use Java or C for writing a compiler, but if you+
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  insist, feel free.}  I will use the current stable version of+
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Scala, which is 2.13.3. If you need a reminder of the Scala handouts+
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for PEP have a look+
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\hr{http://talisker.nms.kcl.ac.uk/cgi-bin/repos.cgi/pep-material/raw-file/tip/handouts/pep-ho.pdf}\bigskip+
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+
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\noindent+
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The main difference to the Scala I showed you in PEP is that in CFL+
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I will use the Ammonite REPL+
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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 2.2.0 (Scala 2.13.3 Java 9)+
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scala> 1 + 2 +
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res0: Int = 3+
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\end{lstlisting} %% $+
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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}.+
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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 ammonite.ops._+
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  +
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scala> read(pwd / "file.name")   +
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res1: String = """..."""+
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+
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scala> write.over(pwd / "file.name", "foo bar")+
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\end{lstlisting}+
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+
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\noindent+
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The latter 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. For loading and accessing code from another Scala file, you+
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can import it 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}  %% $+
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+
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\noindent+
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This assumes the other Scala file is called+
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\texttt{name-of-the-file.sc} and requires the file to be in the same+
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directory where \texttt{amm} is working in. This will be very convenient +
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for the compiler we implement in CFL, because it allows us to easily+
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break up the code into the lexer, parser and code generator.+
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+
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Another feature which exists in Ammonite, but not yet in the+
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current version of Scala (it will be in the next version called dotty)+
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is that you can mark functions as \texttt{@main}. For example+
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+
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\begin{lstlisting}[numbers=none,language=Scala]+
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@main+
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def foo() = ...+
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\end{lstlisting}+
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+
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\noindent+
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This means you can now call that function from the command line like+
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+
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\begin{lstlisting}[numbers=none,language=Scala]+
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$ 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} %% $+
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+
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\noindent+
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What is also good in Ammonite that you can specify more than one+
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function to be ``main'' and then specify on the command line which+
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function you want to run as entry-point.+
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+
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Another feature you might like to use is that Ammonite can ``watch'' files.+
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This means it can automatically re-run a file when it is saved. For this+
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you have to call \texttt{amm} with the option \texttt{-w}, as in+
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+
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\begin{lstlisting}[numbers=none,language=Scala]+
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$ 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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\bigskip+
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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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