1 \documentclass[../thesis.tex
]{subfiles
}
3 \input{subfilepreamble
}
8 \chapter{The
\texorpdfstring{\gls{MTASK
}}{mTask
} language
}%\texorpdfstring{\glsxtrshort{DSL}}{DSL}}%
10 \begin{chapterabstract
}
11 \noindent This chapter introduces the
\gls{TOP
} language
\gls{MTASK
} language by:
13 \item introducing the setup of the
\gls{EDSL
};
14 \item and showing the language interface and examples for the type system, data types, expressions, tasks and their combinators.
18 The
\gls{MTASK
} system is a complete
\gls{TOP
} programming environment for programming microcontrollers.
19 This means that it not only contains a
\gls{TOP
} language but also a
\gls{TOP
} engine.
20 It is implemented as an
\gls{EDSL
} in
\gls{CLEAN
} using class-based---or tagless-final---embedding (see
\cref{sec:tagless-final_embedding
}).
21 Due to the nature of the embedding technique, it is possible to have multiple interpretations for programs written in the
\gls{MTASK
} language.
22 Not all of these intepretations are necessarily
\gls{TOP
} engines, some may perform an analysis over the program or typeset the program so that the output can be shown after evaluating the expression at run time.
23 The following interpretations are available for
\gls{MTASK
}.
28 This interpretation converts the expression to a string representation.
29 As the host language
\gls{CLEAN
} constructs the
\gls{MTASK
} expressions at run time, it can be useful to show the constructed expression.
32 The simulator converts the expression to a ready-for-work
\gls{ITASK
} simulation in which the user can inspect and control the simulated peripherals and see the internal state of the tasks.
33 \item[Byte code compiler
]
35 The compiler compiles the
\gls{MTASK
} program to a specialised byte code.
36 Using a handful of integration functions and tasks (see
\cref{chp:integration_with_itask
}),
\gls{MTASK
} tasks can be executed on microcontrollers and integrated in
\gls{ITASK
} as if they were regular
\gls{ITASK
} tasks.
37 Furthermore, with special language constructs,
\glspl{SDS
} can be shared between
\gls{MTASK
} and
\gls{ITASK
} programs.
40 When using the byte code compiler interpretation in conjunction with the
\gls{ITASK
} integration,
\gls{MTASK
} is a heterogeneous
\gls{DSL
}.
41 I.e.\ some components---e.g.\ the
\gls{RTS
} on the microcontroller---is largely unaware of the other components in the system, and it is executed on a completely different architecture.
42 The
\gls{MTASK
} language is an enriched simply-typed $
\lambda$-calculus with support for some basic types, arithmetic operations, and function definition; and a task language (see
\cref{sec:top
}).
45 To leverage the type checker of the host language, types in the
\gls{MTASK
} language are expressed as types in the host language, to make the language type safe.
46 However, not all types in the host language are suitable for microcontrollers that may only have
\qty{2}{\kibi\byte} of
\gls{RAM
} so class constraints are therefore added to the
\gls{DSL
} functions.
47 The most used class constraint is the
\cleaninline{type
} class collection containing functions for serialization, printing,
\gls{ITASK
} constraints,
\etc.
48 Many of these functions can be derived using generic programming.
49 An even stronger restriction on types is defined for types that have a stack representation.
50 This
\cleaninline{basicType
} class has instances for many
\gls{CLEAN
} basic types such as
\cleaninline{Int
},
\cleaninline{Real
} and
\cleaninline{Bool
}.
51 The class constraints for values in
\gls{MTASK
} are omnipresent in all functions and therefore often omitted throughout throughout the chapters for brevity and clarity.
55 \caption{Translation from
\gls{CLEAN
}/
\gls{MTASK
} data types to
\gls{CPP
} datatypes.
}%
56 \label{tbl:mtask-c-datatypes
}
59 \gls{CLEAN
}/
\gls{MTASK
} &
\gls{CPP
} type &
\textnumero{}bits\\
61 \cleaninline{Bool
} &
\cinline{bool
} &
16\\
62 \cleaninline{Char
} &
\cinline{char
} &
16\\
63 \cleaninline{Int
} &
\cinline{int16_t
} &
16\\
64 \cleaninline{Real
} &
\cinline{float
} &
32\\
65 \cleaninline{:: Long
} &
\cinline{int32_t
} &
32\\
66 \cleaninline{:: T = A \| B \| C
} &
\cinline{enum
} &
16\\
71 \Cref{lst:constraints
} contains the definitions for the auxiliary types and type constraints (such as
\cleaninline{type
} and
\cleaninline{basicType
}) that are used to construct
\gls{MTASK
} expressions.
72 The
\gls{MTASK
} language interface consists of a core collection of type classes bundled in the type class
\cleaninline{class mtask
}.
73 Every interpretation implements the type classes in the
\cleaninline{mtask
} class
74 There are also
\gls{MTASK
} extensions that not every interpretation implements such as peripherals and
\gls{ITASK
} integration.
75 \begin{lstClean
}[caption=
{Classes and class collections for the
\gls{MTASK
} language.
},label=
{lst:constraints
}]
76 class type t | iTask, ... ,fromByteCode, toByteCode t
77 class basicType t | type t where ...
79 class mtask v | expr, ..., int, real, long v
82 Sensors,
\glspl{SDS
}, functions,
\etc{} may only be defined at the top level.
83 The
\cleaninline{Main
} type is used that is used to distinguish the top level from the main expression.
84 Some top level definitions, such as functions, are defined using
\gls{HOAS
}.
85 To make their syntax friendlier, the
\cleaninline{In
} type---an infix tuple---is used to combine these top level definitions as can be seen in
\cleaninline{someTask
} (
\cref{lst:mtask_types
}).
87 \begin{lstClean
}[caption=
{Example task and auxiliary types in the
\gls{MTASK
} language.
},label=
{lst:mtask_types
}]
88 :: Main a =
{ main :: a
}
89 :: In a b = (In) infix
0 a b
91 someTask :: MTask v Int | mtask v & liftsds v & sensor1 v & ...
93 sensor1 config1
\sns1->
94 sensor2 config2
\sns2->
95 sds
\s1 = initialValue
96 In liftsds
\s2 = someiTaskSDS
99 In
{ main = mainexpr
}
102 \Gls{MTASK
} expressions are usually overloaded in their interpretation (
\cleaninline{v
}).
103 In
\gls{CLEAN
}, all free variables in a type are implicitly universally quantified.
104 In order to use the
\gls{MTASK
} expressions with multiple interpretations, rank-
2 polymorphism is required
\citep{odersky_putting_1996
}\citep[\citesection{3.7.4}]{plasmeijer_clean_2021
}.
105 \Cref{lst:rank2_mtask
} shows an example of a function that simulates an
\gls{MTASK
} expression while showing the pretty printed representation in parallel.
106 Providing a type for the
\cleaninline{simulateAndPrint
} function is mandatory as the compiler cannot infer the type of rank-
2 polymorphic functions.
108 \begin{lstClean
}[label=
{lst:rank2_mtask
},caption=
{Rank-
2 polymorphism to allow multiple interpretations
}]
109 prettyPrint :: Main (MTask PrettyPrint a) -> String
110 simulate :: Main (MTask Simulate a) -> Task a
112 simulateAndPrint :: (A.v: Main (MTask v a) | mtask v) -> Task a | type a
113 simulateAndPrint mt =
115 -|| Hint "Current task:" @>> viewInformation
[] (prettyPrint mt)
118 \section{Expressions
}\label{sec:expressions
}
119 This section shows all
\gls{MTASK
} constructs for exppressions.
120 \Cref{lst:expressions
} shows the
\cleaninline{expr
} class containing the functionality to lift values from the host language to the
\gls{MTASK
} language (
\cleaninline{lit
}); perform number and boolean arithmetics; do comparisons; and conditional execution.
121 For every common boolean and arithmetic operator in the host language, an
\gls{MTASK
} variant is present, suffixed by a period to not clash with
\gls{CLEAN
}'s builtin operators.
123 \begin{lstClean
}[caption=
{The
\gls{MTASK
} class for expressions
},label=
{lst:expressions
}]
125 lit :: t -> v t | type t
126 (+.) infixl
6 :: (v t) (v t) -> v t | basicType, +, zero t
128 (&.) infixr
3 :: (v Bool) (v Bool) -> v Bool
129 (|.) infixr
2 :: (v Bool) (v Bool) -> v Bool
130 Not :: (v Bool) -> v Bool
131 (==.) infix
4 :: (v a) (v a) -> v Bool | Eq, basicType a
133 If :: (v Bool) (v t) (v t) -> v t | type t
136 Conversion to-and-fro data types is available through the overloaded functions
\cleaninline{int
},
\cleaninline{long
} and
\cleaninline{real
} that will convert the argument to the respective type similar to casting in
\gls{C
}.
137 For most interpretations, there are instances of these classes for all numeric types.
139 \begin{lstClean
}[caption=
{Type conversion functions in
\gls{MTASK
}.
}]
140 class int v a :: (v a) -> v Int
141 class real v a :: (v a) -> v Real
142 class long v a :: (v a) -> v Long
145 Values from the host language must be explicitly lifted to the
\gls{MTASK
} language using the
\cleaninline{lit
} function.
146 For convenience, there are many lower-cased macro definitions for often used constants such as
\cleaninline{true :== lit True
},
\cleaninline{false :== lit False
},
\etc.
148 \Cref{lst:example_exprs
} shows some examples of these expressions.
149 Since they are only expressions, there is no need for a
\cleaninline{Main
}.
150 \cleaninline{e0
} defines the literal $
42$,
\cleaninline{e1
} calculates the literal $
42.0$ using real numbers.
151 \cleaninline{e2
} compares
\cleaninline{e0
} and
\cleaninline{e1
} as integers and if they are equal it returns the
\cleaninline{e2
}$/
2$ and
\cleaninline{e0
} otherwise.
153 \begin{lstClean
}[label=
{lst:example_exprs
},caption=
{Example
\gls{MTASK
} expressions.
}]
157 e1 :: v Real | expr v
158 e1 = lit
38.0 + real (lit
4)
161 e2 = if' (e0 ==. int e1)
165 \Gls{MTASK
} is shallowly embedded in
\gls{CLEAN
} and the terms are constructed at runtime.
166 This means that
\gls{MTASK
} programs can also be tailor-made at runtime or constructed using
\gls{CLEAN
} functions maximising the linguistic reuse
\citep{krishnamurthi_linguistic_2001
}
167 \cleaninline{approxEqual
} in
\cref{lst:example_macro
} performs a simple approximate equality---albeit without taking into account all floating point pecularities.
168 When calling
\cleaninline{approxEqual
} in an
\gls{MTASK
} function, the resulting code is inlined.
170 \begin{lstClean
}[label=
{lst:example_macro
},caption=
{Example linguistic reuse in the
\gls{MTASK
} language.
}]
171 approxEqual :: (v Real) (v Real) (v Real) -> v Real | expr v
172 approxEqual x y eps = if' (x ==. y) true
179 \subsection{Data types
}
180 Most of
\gls{CLEAN
}'s fixed-size basic types are mapped on
\gls{MTASK
} types.
181 However, it can be useful to have access to compound types as well.
182 All types in
\gls{MTASK
} must have a fixed size representation on the stack so sum types are not (yet) supported.
183 While it is possible to lift types using the
\cleaninline{lit
} function, you cannot do anything with the types besides passing them around but they are being produced by some parallel task combinators (see
\cref{sssec:combinators_parallel
}).
184 To be able to use types as first class citizens, constructors and field selectors are required (see
\cref{chp:first-class_datatypes
}).
185 \Cref{lst:tuple_exprs
} shows the scaffolding for supporting tuples in
\gls{MTASK
}.
186 Besides the constructors and field selectors, there is also a helper function available that transforms a function from a tuple of
\gls{MTASK
} expressions to an
\gls{MTASK
} expression of a tuple.
187 Examples for using tuple can be found in
\cref{sec:mtask_functions
}.
189 \begin{lstClean
}[label=
{lst:tuple_exprs
},caption=
{Tuple constructor and field selectors in
\gls{MTASK
}.
}]
191 tupl :: (v a) (v b) -> v (a, b) | type a & type b
192 first :: (v (a, b)) -> v a | type a & type b
193 second :: (v (a, b)) -> v b | type a & type b
195 tupopen f :==
\v->f (first v, second v)
198 \subsection{Functions
}\label{sec:mtask_functions
}
199 Adding functions to the language is achieved by type class to the
\gls{DSL
}.
200 By using
\gls{HOAS
}, both the function definition and the calls to the function can be controlled by the
\gls{DSL
} \citep{pfenning_higher-order_1988,chlipala_parametric_2008
}.
201 The
\gls{MTASK
} only allows first-order functions and does not allow partial function application.
202 This is restricted by using a multi-parameter type class where the first parameter represents the arguments and the second parameter the view.
203 By providing a single instance per function arity instead of providing one instance for all functions and using tuples for the arguments this constraint can be enforced.
204 Also,
\gls{MTASK
} only supports top-level functions which is enforced by the
\cleaninline{Main
} box.
205 The definition of the type class and the instances for an example interpretation (
\cleaninline{:: Inter
}) are as follows:
207 \begin{lstClean
}[caption=
{Functions in
\gls{MTASK
}.
}]
208 class fun a v :: ((a -> v s) -> In (a -> v s) (Main (MTask v u)))
211 instance fun () Inter where ...
212 instance fun (Inter a) Inter | type a where ...
213 instance fun (Inter a, Inter b) Inter | type a, type b where ...
214 instance fun (Inter a, Inter b, Inter c) Inter | type a, ... where ...
218 Deriving how to define and use functions from the type is quite the challenge even though the resulting syntax is made easier using the infix type
\cleaninline{In
}.
219 \Cref{lst:function_examples
} show the factorial function, a tail-call optimised factorial function and a function with zero arguments to demonstrate the syntax.
220 Splitting out the function definition for each single arity means that that for every function arity and combination of arguments, a separate class constraint must be created.
221 Many of the often used functions are already bundled in the
\cleaninline{mtask
} class constraint collection.
222 \cleaninline{factorialtail
} shows a manually added class constraint.
223 Definiting zero arity functions is shown in the
\cleaninline{zeroarity
} expression.
224 Finally,
\cleaninline{swapTuple
} shows an example of a tuple being swapped.
226 % VimTeX: SynIgnore on
227 \begin{lstClean
}[label=
{lst:function_examples
},caption=
{Function examples in
\gls{MTASK
}.
}]
228 factorial :: Main (v Int) | mtask v
230 fun
\fac=(
\i->if' (i <. lit
1)
232 (i *. fac (i -. lit
1)))
233 In
{main = fac (lit
5)
}
235 factorialtail :: Main (v Int) | mtask v & fun (v Int, v Int) v
237 fun
\facacc=(\(acc, i)->if' (i <. lit
1)
239 (fac (acc *. i, i -. lit
1)))
240 In fun
\fac=(
\i->facacc (lit
1, i))
241 In
{main = fac (lit
5)
}
243 zeroarity :: Main (v Int) | mtask v
245 fun
\fourtytwo=(\()->lit
42)
246 In fun
\add=(\(x, y)->x +. y)
247 In
{main = add (fourtytwo (), lit
9)
}
249 swapTuple :: Main (v (Int, Bool)) | mtask v
251 fun
\swap=(tupopen \(x, y)->tupl y x)
252 In
{main = swap (tupl true (lit
42))
}
254 % VimTeX: SynIgnore off
256 \section{Tasks and task combinators
}\label{sec:top
}
257 This section describes
\gls{MTASK
}'s task language.
258 \Gls{MTASK
}'s task language can be divided into three categories, namely
260 \item Basic tasks, in most
\gls{TOP
} systems, the basic tasks are called editors, modelling the interactivity with the user.
261 In
\gls{MTASK
}, there are no
\emph{editors
} in that sense but there is interaction with the outside world through microcontroller peripherals such as sensors and actuators.
262 \item Task combinators provide a way of describing the workflow.
263 They combine one or more tasks into a compound task.
264 \item \glspl{SDS
} in
\gls{MTASK
} can be seen as references to data that can be shared using many-to-many communication and are only accessible from within the task language to ensure atomicity.
267 As
\gls{MTASK
} is integrated with
\gls{ITASK
}, the same stability distinction is made for task values.
268 A task in
\gls{MTASK
} is denoted by the
\gls{DSL
} type synonym shown in
\cref{lst:task_type
}, an expression of the type
\cleaninline{TaskValue a
} in interpretation
\cleaninline{v
}.
270 \begin{lstClean
}[label=
{lst:task_type
},caption=
{Task type in
\gls{MTASK
}.
}]
271 :: MTask v a :== v (TaskValue a)
273 // From the iTask library
279 \subsection{Basic tasks
}
280 The most rudimentary basic tasks are the
\cleaninline{rtrn
} and
\cleaninline{unstable
} tasks.
281 They lift the value from the
\gls{MTASK
} expression language to the task domain either as a stable value or an unstable value.
282 There is also a special type of basic task for delaying execution.
283 The
\cleaninline{delay
} task---given a number of milliseconds---yields an unstable value while the time has not passed.
284 Once the specified time has passed, the time it overshot the planned time is yielded as a stable task value.
285 See
\cref{sec:repeat
} for an example task using
\cleaninline{delay
}.
287 \begin{lstClean
}[label=
{lst:basic_tasks
},caption=
{Function examples in
\gls{MTASK
}.
}]
288 class rtrn v :: (v t) -> MTask v t
289 class unstable v :: (v t) -> MTask v t
290 class delay v :: (v n) -> MTask v n | long v n
293 \subsubsection{Peripherals
}\label{sssec:peripherals
}
294 For every sensor or actuator, basic tasks are available that allow interaction with the specific peripheral.
295 The type classes for these tasks are not included in the
\cleaninline{mtask
} class collection as not all devices nor all language interpretations have such peripherals connected.
297 \Cref{lst:dht,lst:gpio
} show the type classes for
\glspl{DHT
} sensors and
\gls{GPIO
} access.
298 Other peripherals have similar interfaces, they are available in the
\cref{sec:aux_peripherals
}.
299 For the
\gls{DHT
} sensor there are two basic tasks,
\cleaninline{temperature
} and
\cleaninline{humidity
}, that---will given a
\cleaninline{DHT
} object---produce a task that yields the observed temperature in
\unit{\celcius} or relative humidity as a percentage as an unstable value.
300 Currently, two different types of
\gls{DHT
} sensors are supported, the
\emph{DHT
} family of sensors connect through $
1$-wire protocol and the
\emph{SHT
} family of sensors connected using
\gls{I2C
} protocol.
301 Creating such a
\cleaninline{DHT
} object is very similar to creating functions in
\gls{MTASK
} and uses
\gls{HOAS
} to make it type safe.
303 \begin{lstClean
}[label=
{lst:dht
},caption=
{The
\gls{MTASK
} interface for
\glspl{DHT
} sensors.
}]
306 = DHT_DHT Pin DHTtype
308 :: DHTtype = DHT11 | DHT21 | DHT22
310 DHT :: DHTInfo ((v DHT) -> Main (v b)) -> Main (v b) | type b
311 temperature :: (v DHT) -> MTask v Real
312 humidity :: (v DHT) -> MTask v Real
314 measureTemp :: Main (MTask v Real) | mtask v & dht v
315 measureTemp = DHT (DHT_SHT (i2c
0x36))
\dht->
316 {main=temperature dht
}
319 \Gls{GPIO
} access is divided into three classes: analog, digital and pin modes (see
\cref{lst:gpio
}).
320 For all pins and pin modes an
\gls{ADT
} is available that enumerates the pins.
321 The analog
\gls{GPIO
} pins of a microcontroller are connected to an
\gls{ADC
} that translates the voltage to an integer.
322 Analog
\gls{GPIO
} pins can be either read or written to.
323 Digital
\gls{GPIO
} pins only
report a high or a low value.
324 The
\cleaninline{pin
} type class allows functions to be overloaded in either the analog or digital pins, e.g.\ analog pins can be considered as digital pins as well.
326 For digital
\gls{GPIO
} interaction, the
\cleaninline{dio
} type class is used.
327 The first argument of the functions in this class is overloaded, i.e.\ it accepts either an
\cleaninline{APin
} or a
\cleaninline{DPin
}.
328 Analog
\gls{GPIO
} tasks are bundled in the
\cleaninline{aio
} type class.
329 \Gls{GPIO
} pins usually operate according to a certain pin mode that states whether the pin acts as an input pin, an input with an internal pull-up resistor or an output pin.
330 This setting can be applied using the
\cleaninline{pinMode
} class by hand or by using the
\cleaninline{declarePin
} \gls{GPIO
} pin constructor.
331 Setting the pin mode is a task that immediately finisheds and fields a stable unit value.
332 Writing to a pin is also a task that immediately finishes but yields the written value instead.
333 Reading a pin is a task that yields an unstable value---i.e.\ the value read from the actual pin.
335 \begin{lstClean
}[label=
{lst:gpio
},caption=
{The
\gls{MTASK
} interface for
\gls{GPIO
} access.
}]
336 :: APin = A0 | A1 | A2 | A3 | A4 | A5
337 :: DPin = D0 | D1 | D2 | D3 | D4 | D5 | D6 | D7 | D8 | D9 | D10 | ...
338 :: PinMode = PMInput | PMOutput | PMInputPullup
339 :: Pin = AnalogPin APin | DigitalPin DPin
341 class pin p :: p -> Pin
342 instance pin APin, DPin
345 writeA :: (v APin) (v Int) -> MTask v Int
346 readA :: (v APin) -> MTask v Int
348 class dio p v | pin p where
349 writeD :: (v p) (v Bool) -> MTask v Bool
350 readD :: (v p) -> MTask v Bool | pin p
352 class pinMode v where
353 pinMode :: (v PinMode) (v p) -> MTask v () | pin p
354 declarePin :: p PinMode ((v p) -> Main (v a)) -> Main (v a) | pin p
357 \Cref{lst:gpio_examples
} shows two examples of
\gls{MTASK
} tasks using
\gls{GPIO
} pins.
358 \cleaninline{task1
} reads analog
\gls{GPIO
} pin
3.
359 This is a task that never terminates.
360 \cleaninline{task2
} writes the
\cleaninline{true
} (
\gls{ARDUINO
} \arduinoinline{HIGH
}) value to digital
\gls{GPIO
} pin
3.
361 This task finishes immediately after writing to the pin.
363 \begin{lstClean
}[label=
{lst:gpio_examples
},caption=
{\Gls{GPIO
} example in
\gls{MTASK
}.
}]
364 task1 :: MTask v Int | mtask v
365 task1 = declarePin A3 PMInput
\a3->
{main=readA a3
}
367 task2 :: MTask v Int | mtask v
368 task2 = declarePin D3 PMOutput
\d3->
{main=writeD d3 true
}
371 \subsection{Task combinators
}
372 Task combinators are used to combine multiple tasks to describe workflows.
373 There are three main types of task combinators, namely:
375 \item Sequential combinators that execute tasks one after the other, possibly using the result of the left hand side.
376 \item Parallel combinators that execute tasks at the same time combining the result.
377 \item Miscellaneous combinators that change the semantics of a task---e.g.\ repeat it or delay execution.
380 \subsubsection{Sequential
}
381 Sequential task combination allows the right-hand side task to observe the left-hand side task value.
382 All seqential task combinators are expressed in the
\cleaninline{expr
} class and can be---and are by default---derived from the Swiss army knife step combinator
\cleaninline{>>*.
}.
383 This combinator has a single task on the left-hand side and a list of
\emph{task continuations
} on the right-hand side.
384 The list of task continuations is checked every rewrite step and if one of the predicates matches, the task continues with the result of this combination.
385 \cleaninline{>>=.
} is a shorthand for the bind operation, if the left-hand side is stable, the right-hand side function is called to produce a new task.
386 \cleaninline{>>\|.
} is a shorthand for the sequence operation, if the left-hand side is stable, it continues with the right-hand side task.
387 The
\cleaninline{>>~.
} and
\cleaninline{>>..
} combinators are variants of the ones above that ignore the stability and continue on an unstable value as well.
389 \begin{lstClean
}[label=
{lst:mtask_sequential
},caption=
{Sequential task combinators in
\gls{MTASK
}.
}]
390 class step v | expr v where
391 (>>*.) infixl
1 :: (MTask v t)
[Step v t u
] -> MTask v u
392 (>>=.) infixl
0 :: (MTask v t) ((v t) -> MTask v u) -> MTask v u
393 (>>|.) infixl
0 :: (MTask v t) (MTask v u) -> MTask v u
394 (>>~.) infixl
0 :: (MTask v t) ((v t) -> MTask v u) -> MTask v u
395 (>>..) infixl
0 :: (MTask v t) (MTask v u) -> MTask v u
398 = IfValue ((v t) -> v Bool) ((v t) -> MTask v u)
399 | IfStable ((v t) -> v Bool) ((v t) -> MTask v u)
400 | IfUnstable ((v t) -> v Bool) ((v t) -> MTask v u)
404 The following listing shows an example of a step in action.
405 The
\cleaninline{readPinBin
} function produces an
\gls{MTASK
} task that classifies the value of an analogue pin into four bins.
406 It also shows that the nature of embedding allows the host language to be used as a macro language.
409 \begin{lstClean
}[label=
{lst:mtask_readpinbin
},caption=
{Read an analog pin and bin the value in
\gls{MTASK
}.
}]
410 readPinBin :: Int -> Main (MTask v Int) | mtask v
411 readPinBin lim = declarePin PMInput A2
\a2->
412 { main = readA a2 >>*.
413 [ IfValue (
\x->x <. lim) (
\_->rtrn (lit bin))
414 \\ lim <-
[64,
128,
192,
256]
418 \subsubsection{Parallel
}\label{sssec:combinators_parallel
}
419 The result of a parallel task combination is a compound that actually executes the tasks at the same time.
420 There are two types of parallel task combinators (see
\cref{lst:mtask_parallel
}).
422 \begin{lstClean
}[label=
{lst:mtask_parallel
},caption=
{Parallel task combinators in
\gls{MTASK
}.
}]
423 class (.&&.) infixr
4 v :: (MTask v a) (MTask v b) -> MTask v (a, b)
424 class (.||.) infixr
3 v :: (MTask v a) (MTask v a) -> MTask v a
427 The conjunction combinator (
\cleaninline{.&&.
}) combines the result by putting the values from both sides in a tuple.
428 The stability of the task depends on the stability of both children.
429 If both children are stable, the result is stable, otherwise the result is unstable.
430 The disjunction combinator (
\cleaninline{.\|\|.
}) combines the results by picking the leftmost, most stable task.
431 The semantics are most easily described using the
\gls{CLEAN
} functions shown in
\cref{lst:semantics_con,lst:semantics_dis
}.
435 \begin{subfigure
}[t
]{.5\textwidth}
436 \begin{lstClean
}[caption=
{Semantics of the\
\conjunction combinator.
},label=
{lst:semantics_con
}]
437 con :: (TaskValue a) (TaskValue b)
439 con NoValue r = NoValue
440 con l NoValue = NoValue
441 con (Value l ls) (Value r rs)
442 = Value (l, r) (ls && rs)
446 \begin{subfigure
}[t
]{.5\textwidth}
447 \begin{lstClean
}[caption=
{Semantics of the\
\disjunction combinator.
},label=
{lst:semantics_dis
}]
448 dis :: (TaskValue a) (TaskValue a)
452 dis (Value l ls) (Value r rs)
454 | otherwise = Value l ls
459 \Cref{lst:mtask_parallel_example
} gives an example program using the parallel task combinator.
460 This program will read two pins at the same time, returning when one of the pins becomes
\arduinoinline{HIGH
}.
461 If the combinator was the
\cleaninline{.&&.
} instead, the type would be
\cleaninline{MTask v (Bool, Bool)
} and the task would only return when both pins have been
\arduinoinline{HIGH
} but not necessarily at the same time.
463 \begin{lstClean
}[label=
{lst:mtask_parallel_example
},caption=
{Parallel task combinator example in
\gls{MTASK
}.
}]
466 declarePin D0 PMInput
\d0->
467 declarePin D1 PMInput
\d1->
468 let monitor pin = readD pin >>*.
[IfValue (
\x->x)
\x->rtrn x
]
469 In
{main = monitor d0 .||. monitor d1
}
472 \subsubsection{Repeat
}\label{sec:repeat
}
473 The
\cleaninline{rpeat
} combinator executes the child task.
474 If a stable value is observed, the task is reinstated.
475 The functionality of
\cleaninline{rpeat
} can also be simulated by using functions and sequential task combinators and even made to be stateful as can be seen in
\cref{lst:blinkthreadmtask
}.
477 \begin{lstClean
}[label=
{lst:mtask_repeat
},caption=
{Repeat task combinators in
\gls{MTASK
}.
}]
479 rpeat :: (MTask v a) -> MTask v a
482 To demonstrate the combinator,
\cref{lst:mtask_repeat_example
} show
\cleaninline{rpeat
} in use.
483 This task will mirror the value read from analog
\gls{GPIO
} pin
\cleaninline{A1
} to pin
\cleaninline{A2
} by constantly reading the pin and writing the result.
485 \begin{lstClean
}[label=
{lst:mtask_repeat_example
},caption=
{Exemplary repeat task in
\gls{MTASK
}.
}]
486 task :: MTask v Int | mtask v
488 declarePin A1 PMInput
\a1->
489 declarePin A2 PMOutput
\a2->
490 {main = rpeat (readA a1 >>~. writeA a2 >>|. delay (lit
1000))
}
493 \subsection{\texorpdfstring{\Glsxtrlongpl{SDS
}}{Shared data sources
}}
494 \Glspl{SDS
} in
\gls{MTASK
} are by default references to shared memory but can also be references to
\glspl{SDS
} in
\gls{ITASK
} (see
\cref{sec:liftsds
}).
495 Similar to peripherals (see
\cref{sssec:peripherals
}), they are constructed at the top level and are accessed through interaction tasks.
496 The
\cleaninline{getSds
} task yields the current value of the
\gls{SDS
} as an unstable value.
497 This behaviour is similar to the
\cleaninline{watch
} task in
\gls{ITASK
}.
498 Writing a new value to
\pgls{SDS
} is done using
\cleaninline{setSds
}.
499 This task yields the written value as a stable result after it is done writing.
500 Getting and immediately after setting
\pgls{SDS
} is not necessarily an
\emph{atomic
} operation in
\gls{MTASK
} because it is possible that another task accesses the
\gls{SDS
} in between.
501 To circumvent this issue,
\cleaninline{updSds
} is created, this task atomically updates the value of the
\gls{SDS
}.
502 The
\cleaninline{updSds
} task only guarantees atomicity within
\gls{MTASK
}.
504 \begin{lstClean
}[label=
{lst:mtask_sds
},caption=
{\Glspl{SDS
} in
\gls{MTASK
}.
}]
507 sds :: ((v (Sds t)) -> In t (Main (MTask v u))) -> Main (MTask v u)
508 getSds :: (v (Sds t)) -> MTask v t
509 setSds :: (v (Sds t)) (v t) -> MTask v t
510 updSds :: (v (Sds t)) ((v t) -> v t) -> MTask v t
513 \Cref{lst:mtask_sds_examples
} shows an example using
\glspl{SDS
}.
514 The
\cleaninline{count
} function takes a pin and returns a task that counts the number of times the pin is observed as high by incrementing the
\cleaninline{share
} \gls{SDS
}.
515 In the
\cleaninline{main
} expression, this function is called twice and the results are combined using the parallel or combinator (
\cleaninline{.\|\|.
}).
516 Using a sequence of
\cleaninline{getSds
} and
\cleaninline{setSds
} would be unsafe here because the other branch might write their old increment value immediately after writing, effectively missing a count.
\todo{beter opschrijven
}
518 \begin{lstClean
}[label=
{lst:mtask_sds_examples
},caption=
{Examples with
\glspl{SDS
} in
\gls{MTASK
}.
}]
519 task :: MTask v Int | mtask v
520 task = declarePin D3 PMInput
\d3->
521 declarePin D5 PMInput
\d5->
523 In fun
\count=(
\pin->
525 >>*
[IfValue (
\x->x) (
\_->updSds (
\x->x +. lit
1) share)
]
526 >>| delay (lit
100) // debounce
528 In
{main=count d3 .||. count d5
}
532 \Gls{MTASK
} is a rich
\gls{TOP
} language tailored for
\gls{IOT
} systems.
533 It is embedded in the pure functional language
\gls{CLEAN
} and uses an enriched lambda calculus as a host language.
534 It provides support for all common arithmetic expressions, conditionals, functions, but also several basic tasks, task combinators, peripheral support and integration with
\gls{ITASK
}.
535 By embedding domain-specific knowledge in the language itself, it achieves the same abstraction level and dynamicity as other
\gls{TOP
} languages while targetting tiny computers instead.
536 As a result, a single declarative specification can describe an entire
\gls{IOT
} system.
538 \input{subfilepostamble
}