From a0fc5b24e17c83d05fa5cb95e855e784abac8f3e Mon Sep 17 00:00:00 2001
From: Mart Lubbers <mart@martlubbers.net>
Date: Sat, 20 May 2017 12:13:03 +0200
Subject: [PATCH] add a bit about combinators

---
 methods.top.tex | 53 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 52 insertions(+), 1 deletion(-)

diff --git a/methods.top.tex b/methods.top.tex
index 9777db5..174a783 100644
--- a/methods.top.tex
+++ b/methods.top.tex
@@ -67,4 +67,55 @@ specialization instances for these functions and show an according interface.
 Generated interfaces can be modified with decoration operators.
 
 \subsection{Combinators}
-\todo{Stukje over combinators, in ieder geval bind en paralel}
+\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 that
+starts a new task according to the \CI{TaskValue}. The 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 been 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}
+
+\begin{lstlisting}[language=Clean,%
+	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
+:: TaskCont a b
+	=     OnValue             ((TaskValue a)  -> Maybe b)
+	|     OnAction    Action  ((TaskValue a)  -> Maybe b)
+	| E.e: OnException         (e              -> b)       & iTask e
+	|     OnAllExceptions     (String         -> b)
+:: Action = Action String
+
+//Parallel combinators
+(-||-) infixr 3 :: (Task a) (Task a)              -> Task a     | iTask a
+(||-)  infixr 3 :: (Task a) (Task b)              -> Task b     | iTask a & iTask b
+(-||)  infixl 3 :: (Task a) (Task b)              -> Task a     | iTask a & iTask b
+(-&&-) infixr 4 :: (Task a) (Task b)              -> Task (a,b) | iTask a & iTask b
+\end{lstlisting}
+
+\subsection{\acrlongpl{SDS}}
+
-- 
2.20.1