X-Git-Url: https://git.martlubbers.net/?a=blobdiff_plain;f=methods.top.tex;h=9d07eec2e41188182f7960968c077a5cf2aa8a41;hb=a4d108b9046bfd1d94e8b986a00c00090391d7b6;hp=aefa35dba70220a456a8c35d3290adc82716fb03;hpb=66de2590bcb4046b92ea54bcd3e55b38208be17b;p=msc-thesis1617.git diff --git a/methods.top.tex b/methods.top.tex index aefa35d..9d07eec 100644 --- a/methods.top.tex +++ b/methods.top.tex @@ -1,13 +1,13 @@ \section{iTasks} -\gls{TOP} is a modern recent programming paradigm implemented as +\gls{TOP} is a novel programming paradigm implemented as \gls{iTasks}~\cite{achten_introduction_2015} in the pure lazy functional -language \gls{Clean}~\cite{brus_cleanlanguage_1987}. \gls{iTasks} is a +language \gls{Clean}~\cite{brus_cleanlanguage_1987}. \gls{iTasks} is an \gls{EDSL} to model workflow tasks in the broadest sense. A \gls{Task} is just -a function that --- given some state --- returns the observable \CI{TaskValue}. The -\CI{TaskValue} of a \CI{Task} can have different states. Not all state +a function that --- given some state --- returns the observable \CI{TaskValue}. +The \CI{TaskValue} of a \CI{Task} can have different states. Not all state transitions are possible as shown in Figure~\ref{fig:taskvalue}. Once a value -is stable it can never become unstable again. Stability is often reached -by pressing a confirmation button. \glspl{Task} yielding a constant value are +is stable it can never become unstable again. Stability is often reached by +pressing a confirmation button. \glspl{Task} yielding a constant value are immediately stable. A simple \gls{iTasks} example illustrating the route to stability of a @@ -16,7 +16,7 @@ Listing~\ref{lst:taskex}. The code is accompanied by screenshots showing the user interface in Figure~\ref{fig:taskex1},~\ref{fig:taskex2} and~\ref{fig:taskex3}. The \CI{TaskValue} of the \gls{Task} is in the first image in the \CI{NoValue} state, the second image does not have all the fields -filled in and therefore the \CI{TaskValue} remains \CI{Unstable}. In the third +filled in and therefore the \CI{TaskValue} remains \CI{NoValue}. In the third image all fields are entered and the \CI{TaskValue} transitions to the \CI{Unstable} state. When the user presses \emph{Continue} the value becomes \CI{Stable} and cannot be changed any further. @@ -63,47 +63,23 @@ enterName = enterInformation "Enter your name" [] For a type to be suitable, it must have instances for a collection of generic functions that is captured in the class \CI{iTask}. Basic types have -specialization instances for these functions and show an according interface. -Generated interfaces can be modified with decoration operators. +specialization instances for these functions and show an interface accordingly. +Derived interfaces can be modified with decoration operators or specializations +can be created. \section{Combinators} \Glspl{Task} can be combined using so called \gls{Task}-combinators. -Combinators describe relations between \glspl{Task}. \Glspl{Task} can be -combined in parallel, sequenced and their result values can be converted to -\glspl{SDS}. Moreover, a very important combinator is the step combinator which -starts a new \gls{Task} according to specified predicates on the -\CI{TaskValue}. Type signatures of the basic combinators are shown in -Listing~\ref{lst:combinators}. - -\begin{itemize} - \item Step: - - The step combinator is used to start \glspl{Task} when a predicate on - the \CI{TaskValue} holds or an action has taken place. The bind - operator can be written as a step combinator. - \begin{lstlisting}[language=Clean] -(>>=) infixl 1 :: (Task a) (a -> (Task b)) -> (Task b) | iTask a & iTask b -(>>=) ta f = ta >>* [OnAction "Continue" onValue, OnValue onStable] - where - onValue (Value a _) = Just (f a) - onValue _ = Nothing - - onStable (Value a True) = Just (f a) - onStable _ = Nothing - \end{lstlisting} - \item Parallel: - - The parallel combinator allows for concurrent \glspl{Task}. The - \glspl{Task} combined with these operators will appear at the same time - in the web browser of the user and the results are combined as the type - dictates. -\end{itemize} +Combinators describe relations between \glspl{Task}. There are only two basic +types of combinators; parallel and sequence. All other combinators are +derived from the basic combinators. Type signatures of simplified versions of +the basic combinators and their derivations are given in +Listing~\ref{lst:combinators} \begin{lstlisting}[% caption={\Gls{Task}-combinators},label={lst:combinators}] //Step combinator -(>>*) infixl 1 :: (Task a) [TaskCont a (Task b)] -> Task b | iTask a & iTask b (>>=) infixl 1 :: (Task a) (a -> Task b) -> Task b | iTask a & iTask b +(>>*) infixl 1 :: (Task a) [TaskCont a (Task b)] -> Task b | iTask a & iTask b :: TaskCont a b = OnValue ((TaskValue a) -> Maybe b) | OnAction Action ((TaskValue a) -> Maybe b) @@ -118,14 +94,43 @@ Listing~\ref{lst:combinators}. (-&&-) infixr 4 :: (Task a) (Task b) -> Task (a,b) | iTask a & iTask b \end{lstlisting} +\paragraph{Sequence:} +The implementation for the sequence combinator is called the +\CI{step} (\CI{>>*}). This combinator runs the left-hand \gls{Task} and +starts the right-hand side when a certain predicate holds. Predicates +can be propositions about the \CI{TaskValue}, user actions from within +the web browser or a thrown exception. The familiar +bind-combinator is an example of a sequence combinator. This combinator +runs the left-hand side and continues to the right-hand \gls{Task} if +there is an \CI{UnStable} value and the user presses continue or when +the value is \CI{Stable}. The combinator could have been implemented +as follows: +\begin{lstlisting}[language=Clean] +(>>=) infixl 1 :: (Task a) (a -> (Task b)) -> (Task b) | iTask a & iTask b +(>>=) ta f = ta >>* [OnAction "Continue" onValue, OnValue onStable] + where + onValue (Value a _) = Just (f a) + onValue _ = Nothing + + onStable (Value a True) = Just (f a) + onStable _ = Nothing +\end{lstlisting} + +\paragraph{Parallel:} +The parallel combinator allows for concurrent \glspl{Task}. The +\glspl{Task} combined with these operators will appear at the same time +in the web browser of the user and the results are combined as the type +dictates. All parallel combinators used are derived from the basic parallel +combinator that is very complex and only used internally. + \section{Shared Data Sources} \Glspl{SDS} are an abstraction over resources that are available in the world or in the \gls{iTasks} system. The shared data can be a file on disk, the system time, a random integer or just some data stored in memory. The actual \gls{SDS} is just a record containing functions on how to read and write the source. In these functions the \CI{*IWorld} --- which in turn contains the real -program \CI{*World} --- is available. Accessing the outside world is required -for interacting with it and thus the functions can access files on disk, raw +\CI{*World} --- is available. Accessing the outside world is required for +interacting with it and thus the functions can access files on disk, raw memory, other \glspl{SDS} and hardware. The basic operations for \glspl{SDS} are get, set and update. The signatures @@ -136,8 +141,8 @@ shares residing in memory are available as well. The three main operations on shares are atomic in the sense that during reading no other \glspl{Task} are executed. The system provides useful functions to transform, map and combine \glspl{SDS} using combinators. The system also provides functionality to -inspect the value of a \gls{SDS} and act upon a change. \Glspl{Task} waiting on -a \gls{SDS} to change are notified when needed. This results in low resource +inspect the value of an \gls{SDS} and act upon a change. \Glspl{Task} waiting on +an \gls{SDS} to change are notified when needed. This results in low resource usage because \glspl{Task} are never constantly inspecting \gls{SDS} values but are notified. @@ -166,25 +171,25 @@ resource are notified of the update. However, it may be the case that To solve this problem, parametric lenses were introduced~\cite{domoszlai_parametric_2014}. -Parametric lenses add a type variable to the \gls{SDS} that is in the current -library functions fixed to the void type (i.e. \CI{()}). When a \gls{SDS} +Parametric lenses add a type variable to the \gls{SDS}. This type variable is +fixed to the void type (i.e. \CI{()}) in the given functions. When an \gls{SDS} executes a write operation, it also provides the system with a notification predicate. This notification predicate is a function \CI{p -> Bool} where \CI{p} is the parametric lens type. This allows programmers to create a big \gls{SDS}, and have \glspl{Task} only look at parts of the big \gls{SDS}. This technique is used in the current system in memory shares. The \CI{IWorld} -contains a map that is accessible through a \gls{SDS}. While all data is +contains a map that is accessible through an \gls{SDS}. While all data is stored in the map, only \glspl{Task} looking at a specific entry are notified when the structure is updated. The type of the parametric lens is the key in the map. -Functionality for setting parameters is added in the system. The most important -functions are the \CI{sdsFocus} and the \CI{sdsLens} function. These functions -are listed in Listing~\ref{lst:focus}. \CI{sdsFocus} allows the programmer to -fix a parametric lens value. \CI{sdsLens} is a kind of \CI{mapReadWrite} -including access to the parametric lens value. This allows the creation of -for example \glspl{SDS} that only read and write to parts of the original -\gls{SDS}. +Functionality for setting parameters is available in the system. The most +important functions are the \CI{sdsFocus} and the \CI{sdsLens} function. These +functions are listed in Listing~\ref{lst:focus}. \CI{sdsFocus} allows the +programmer to fix a parametric lens value. \CI{sdsLens} is a kind of +\CI{mapReadWrite} including access to the parametric lens value. This allows +the creation of, for example, \glspl{SDS} that only read and write to parts of +the original \gls{SDS}. \begin{lstlisting}[label={lst:focus}, caption={Parametric lens functions}]