Rephrase TamedFJ intro
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tRules.tex
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tRules.tex
@ -7,36 +7,48 @@
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% the constraint generation step assumes every method argument to be encapsulated in a let statement. This is the way Java is doing capture conversion
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The input to our algorithm is a typeless version of Featherweight Java.
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The syntax is shown in figure \ref{fig:syntax}
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and the respective type rules in figure \ref{fig:expressionTyping} and \ref{fig:typing}.
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Method parameters and return types are optional.
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We still require type annotations for fields and generic class parameters.
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The syntax is shown in figure \ref{fig:syntax} with optional type annotations highlighted in yellow.
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The respective type rules are defined by figure \ref{fig:expressionTyping} and \ref{fig:typing}.
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\TamedFJ{} is a subset of the calculus defined by \textit{Bierhoff} \cite{WildcardsNeedWitnessProtection}.
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The point is that a correct and fully typed \TamedFJ{} program is also a correct Featherweight Java program,
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which is vital for our soundness proof (see chapter \ref{sec:soundness}).
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%The language is designed to showcase type inference involving existential types.
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This calculus is used as input aswell as output to our global type inference algorithm.
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We assume that the input to our algorithm is a program, which carries none of the optional type annotations.
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After calculating a type solution we can insert all missing types and generate a correct program.
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A method assumption consists out of a method name, a list of type parameters, a list of argument types, and a return type.
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The first argument type is the type of the surrounding class or the \texttt{this} parameter one could say.
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For example the \texttt{add} method in listing \ref{lst:tamedfjSample} is represented by the assumption
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$\texttt{add} : \generics{\ol{X \triangleleft Object}}\ \type{X} \to \exptype{List}{\type{X}}$.
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\begin{lstlisting}[style=java,caption=\TamedFJ{} sample, label=lst:tamedfjSample]
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class List<A extends Object> {
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List<A> add(A v){..,}
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}
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\end{lstlisting}
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TODO
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\\[1em]
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\noindent
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\textit{Additional Notes:}%
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\begin{itemize}
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\item Method parameters and return types are optional.
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\item We still require type annotations for fields and generic class parameters.
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This is a design choice by us,
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as we consider them as data declarations which are given by the programmer.
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% They are inferred in for example \cite{plue14_3b}
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Note the \texttt{new} expression not requiring generic parameters,
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which are also inferred by our algorithm.
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The method call naturally has type inferred generic parameters aswell.
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We add the elvis operator ($\elvis{}$) to the syntax mainly to showcase applications involving wildcard types.
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The syntax is described in figure \ref{fig:syntax} with optional type annotations highlighted in yellow.
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It is possible to exclude all optional types.
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\TamedFJ{} is a subset of the calculus defined by \textit{Bierhoff} \cite{WildcardsNeedWitnessProtection}.
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%The language is designed to showcase type inference involving existential types.
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The idea is for our type inference algorithm to calculate all missing types and output a fully and correctly typed \TamedFJ{} program,
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which by default is also a correct Featherweight Java program (see chapter \ref{sec:soundness}).
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\noindent
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\textit{Notes:}
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\begin{itemize}
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\item The calculus does not include method overriding for simplicity reasons.
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\item We add the elvis operator ($\elvis{}$) to the syntax mainly to showcase applications involving wildcard types.
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\item \textit{Note:} The \texttt{new} expression is not requiring generic parameters.
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\item Every method has an unique name.
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The calculus does not include method overriding for simplicity reasons.
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Type inference for that is described in \cite{TIforFGJ} and can be added to this algorithm accordingly.
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%\textit{Note:}
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\item The \textsc{T-Program} type rule ensures that there is one set of method assumptions used for all classes
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that are part of the program.
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\item The typing rules for expressions shown in figure \ref{fig:expressionTyping} refrain from restricting polymorphic recursion.
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Type inference for polymorphic recursion is undecidable \cite{wells1999typability} and when proving completeness like in \cite{TIforFGJ} the calculus
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needs to be restricted in that regard.
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Our algorithm is not complete (see discussion in chapter \ref{sec:completeness}) and without the respective proof we can keep the \TamedFJ{} calculus as simple as possible
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and as close to it's Featherweight Java correspondent \cite{WildcardsNeedWitnessProtection} as possible.
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Our soundness proof works either way.
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and as close to it's Featherweight Java correspondent as possible,
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simplifying the soundness proof.
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\end{itemize}
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%Additional features like overriding methods and method overloading can be added by copying the respective parts from there.
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