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‎corout.fdoc

Lines changed: 7 additions & 153 deletions
Original file line numberDiff line numberDiff line change
@@ -276,102 +276,15 @@ when there is nothing left to do precisely because it's just another
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coroutine.
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@h2 Running subsystems
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So far we have worked with the main scheduler, which terminates when there
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is nothing left to do. So I want to show you a little problem and
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how to solve it:
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@tangle ex4
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var x = list[int] (1,2,3,4,5);
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fun addup (acc: int) (elt:int) => acc + elt;
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var y = fold_left addup 0 x;
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println$ y;
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@
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This is the purely functional way to add up a list. It is a client server application
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where the fold operation is the service provider and the @{addup}
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function is the client. However the technical implementation has a severe
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problem: the client if forced to write a function to do the work, which can
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only handle one element at a time, and has a single state variable, @{acc},
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the accumulator. In other words, the client has to provide a callback,
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which is a slave to master fold routine.
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Here is another way to do the same thing:
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@tangle ex4
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var acc = 0;
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for elt in x do
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acc = acc + elt;
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done
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@
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In this case we're using an iterator over the list which is provided
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by the library, and that iterator is a slave to the client code
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which is master: the iterator is called by the client.
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Both these solutions work, and they are in fact dual or <em>control inverse</em>:
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each one is the other one turned inside out with respect to control relations.
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The client is a slave in the first solution whilst the iterator is a slave
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in the second.
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There is way to do this without slavery .. using coroutines of course!
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@tangle ex4
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begin
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chip adder connector io pin inp: %<int {
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var acc = 0;
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while true do
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var elt = read io.inp;
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acc = acc + elt;
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println$ acc;
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done
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}
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(source_from_list x |-> adder)();
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end
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@
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The chip @{source_from_list} comes from the standard library, it just writes
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each element of a list down its output channel.
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The code terminates when you expect and the last result printed is the answer.
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But we just want the answer!
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So here is our first attempt:
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@tangle ex4
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begin
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var acc = 0;
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chip adder connector io pin inp: %<int {
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while true do
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sleep (0.025);
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var elt = read io.inp;
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acc = acc + elt;
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done
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}
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(source_from_list x |-> adder)();
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println$ "Attempt1: " + acc.str;
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end
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@
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Of course this doesn't work we get:
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@pre
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Attempt1: 0
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@
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because as we know, the mainline is a coroutine, and it continues on whilst
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the @{adder} is sleeping. In the abstract semantics when there is a set
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of coroutines waiting to run, the scheduler can run <em>any one</em> of them
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so even without the sleep, it could complete the mainline before completing
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the pipeline.
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@tangle ex4
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begin
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var acc = 0;
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chip adder connector io pin inp: %<int {
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while true do
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var elt = read io.inp;
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acc = acc + elt;
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done
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}
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run (source_from_list x |-> adder);
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println$ "Attempt2: " + acc.str;
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end
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@
279+
There is a constraint on Felix coroutines: they have to be procedures.
280+
Functions cannot read and write channels. However there is a way around
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this problem: you can use the @{run} subroutine to create an run a new,
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nested, scheduler.
373283

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The @{run} subroutine, being a subroutine, returns when it is finished.
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Unfortunately there is another constraint on nested schedulers: they cannot
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do asynchronous I/O.
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@h1 The concept of fibration
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A <em>coroutine system</em> is a collection of processes called <em>fibres</em>
@@ -447,62 +360,3 @@ to give it a chance to actually fetch the data before the write
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might modify it.
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@h2 next
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stuff
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@felix
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blah
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@
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stuff
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@h1 high
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blam
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@h2 med1
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stuff
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stuff
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stuff
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stuff
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stuff
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stuff
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@h2 med2
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stuff
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@h2 med3
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stuff <em>inline html works</em>
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but we have @{micros} for inline code as well.
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<a href= https://www.itkservices2.com/nem_review_1.2>See ITK stuff</a>
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@h3 low
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level 3 stuff
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@felix
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blah
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@
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stuff
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‎corout.html

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Tangler filename=examples/ex3.flx
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Extension=.flx
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flx ....
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Tangle id=ex4
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Tangler filename=examples/ex4.flx
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Extension=.flx
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flx ....
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Tangle id=ex4
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Tangler filename=examples/ex4.flx
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Extension=.flx
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flx ....
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Tangle id=ex4
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Tangler filename=examples/ex4.flx
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Extension=.flx
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flx ....
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Tangle id=ex4
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Tangler filename=examples/ex4.flx
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Extension=.flx
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flx ....
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Tangle id=ex4
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Tangler filename=examples/ex4.flx
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Extension=.flx
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flx ....
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<html><head>
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<style type="text/css">
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body {margin:3%; }
@@ -384,13 +364,7 @@
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"Asynchronous I/O",
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"Felix is a coroutine",
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"Running subsystems",
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"The concept of fibration",
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"next",
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"high",
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"med1",
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"med2",
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"med3",
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"low"
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"The concept of fibration"
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];
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function expand_all(dummy)
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{
@@ -468,15 +442,8 @@
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</div>
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<div class=m1 onclick="mshow('menu4','#The concept of fibration_h')"> <a href="#The_concept_of_fibration_h">The concept of fibration</a></div>
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<div class=sm id=menu4>
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<div class=m2><a href="#next_h">next</a></div>
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</div>
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<div class=m1 onclick="mshow('menu5','#high_h')"> <a href="#high_h">high</a></div>
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<div class=sm id=menu5>
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<div class=m2><a href="#med1_h">med1</a></div>
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<div class=m2><a href="#med2_h">med2</a></div>
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<div class=m2><a href="#med3_h">med3</a></div>
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</div>
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<script>counter_max=5;</script>
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<script>counter_max=4;</script>
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</div>
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<!--End Left Margin Toc-->
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@@ -728,92 +695,14 @@ <h1 id='A_low_level_example._h'><img src='/share/src/web/images/minus.gif' id='A
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when there is nothing left to do precisely because it's just another
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coroutine.
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</p></div><h2 id='Running_subsystems_h'><img src='/share/src/web/images/minus.gif' id='Running subsystems' onclick='toggle(this,"Running_subsystems_d")' alt='+'/> 3.2 Running subsystems</h2><div id='Running_subsystems_d' style='display:block'>
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<p>So far we have worked with the main scheduler, which terminates when there
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is nothing left to do. So I want to show you a little problem and
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how to solve it:
734-
</p><pre class='inclusion'>
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examples/ex4.flx</pre>
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<p><pre class='flxbg'><span class="lineno" id=line1></span> <span class="big_keyword" title="Define a mutable variable">var</span> x = <span class="library" title="functional, singly linked list">list</span>[<span class="library" title="binding of C int type">int</span>] (1,2,3,4,5);
737-
<span class="lineno" id=line2></span> <span class="big_keyword" title="Define a function with no side-effects">fun</span> addup (acc: <span class="library" title="binding of C int type">int</span>) (elt:<span class="library" title="binding of C int type">int</span>) =&gt; acc + elt;
738-
<span class="lineno" id=line3></span> <span class="big_keyword" title="Define a mutable variable">var</span> y = <span class="library" title="accumulated values of data structure from left into initial value using function">fold_left</span> addup 0 x;
739-
<span class="lineno" id=line4></span> <span class="library" title="Print a string to standard output with newline appended">println</span>$ y;
740-
</pre></p><p>This is the purely functional way to add up a list. It is a client server application
741-
where the fold operation is the service provider and the <code>addup</code>
742-
function is the client. However the technical implementation has a severe
743-
problem: the client if forced to write a function to do the work, which can
744-
only handle one element at a time, and has a single state variable, <code>acc</code>,
745-
the accumulator. In other words, the client has to provide a callback,
746-
which is a slave to master fold routine.
747-
</p><p>Here is another way to do the same thing:
748-
</p><pre class='inclusion'>
749-
examples/ex4.flx</pre>
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<p><pre class='flxbg'><span class="lineno" id=line1></span> <span class="big_keyword" title="Define a mutable variable">var</span> acc = 0;
751-
<span class="lineno" id=line2></span> <span class="small_keyword" title="for loop">for</span> elt <span class="small_keyword" title="membership operator, function mem">in</span> x <span class="small_keyword" title="imperative code begins">do</span>
752-
<span class="lineno" id=line3></span> acc = acc + elt;
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<span class="lineno" id=line4></span> <span class="small_keyword" title="end of body">done</span>
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</pre></p><p>In this case we're using an iterator over the list which is provided
755-
by the library, and that iterator is a slave to the client code
756-
which is master: the iterator is called by the client.
757-
</p><p>Both these solutions work, and they are in fact dual or <em>control inverse</em>:
758-
each one is the other one turned inside out with respect to control relations.
759-
The client is a slave in the first solution whilst the iterator is a slave
760-
in the second.
761-
</p><p>There is way to do this without slavery .. using coroutines of course!
762-
</p><pre class='inclusion'>
763-
examples/ex4.flx</pre>
764-
<p><pre class='flxbg'><span class="lineno" id=line1></span> <span class="small_keyword" title="end of extension">begin</span>
765-
<span class="lineno" id=line2></span> chip adder connector io pin inp: %&lt;<span class="library" title="binding of C int type">int</span> {
766-
<span class="lineno" id=line3></span> <span class="big_keyword" title="Define a mutable variable">var</span> acc = 0;
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<span class="lineno" id=line4></span> <span class="small_keyword" title="while loop">while</span> <span class="library" title="truth value">true</span> <span class="small_keyword" title="imperative code begins">do</span>
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<span class="lineno" id=line5></span> <span class="big_keyword" title="Define a mutable variable">var</span> elt = read io.inp;
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<span class="lineno" id=line6></span> acc = acc + elt;
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<span class="lineno" id=line7></span> <span class="library" title="Print a string to standard output with newline appended">println</span>$ acc;
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<span class="lineno" id=line8></span> <span class="small_keyword" title="end of body">done</span>
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<span class="lineno" id=line9></span> }
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<span class="lineno" id=line10></span> (source_from_list x |-&gt; adder)();
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<span class="lineno" id=line11></span> <span class="small_keyword" title="end of extension">end</span>
775-
</pre></p><p>The chip <code>source_from_list</code> comes from the standard library, it just writes
776-
each element of a list down its output channel.
777-
</p><p>The code terminates when you expect and the last result printed is the answer.
778-
But we just want the answer!
779-
</p><p>So here is our first attempt:
780-
</p><pre class='inclusion'>
781-
examples/ex4.flx</pre>
782-
<p><pre class='flxbg'><span class="lineno" id=line1></span> <span class="small_keyword" title="end of extension">begin</span>
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<span class="lineno" id=line2></span> <span class="big_keyword" title="Define a mutable variable">var</span> acc = 0;
784-
<span class="lineno" id=line3></span> chip adder connector io pin inp: %&lt;<span class="library" title="binding of C int type">int</span> {
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<span class="lineno" id=line4></span> <span class="small_keyword" title="while loop">while</span> <span class="library" title="truth value">true</span> <span class="small_keyword" title="imperative code begins">do</span>
786-
<span class="lineno" id=line5></span> sleep (0.025);
787-
<span class="lineno" id=line6></span> <span class="big_keyword" title="Define a mutable variable">var</span> elt = read io.inp;
788-
<span class="lineno" id=line7></span> acc = acc + elt;
789-
<span class="lineno" id=line8></span> <span class="small_keyword" title="end of body">done</span>
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<span class="lineno" id=line9></span> }
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<span class="lineno" id=line10></span>
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<span class="lineno" id=line11></span> (source_from_list x |-&gt; adder)();
793-
<span class="lineno" id=line12></span> <span class="library" title="Print a string to standard output with newline appended">println</span>$ <span class="fstring">"Attempt1: "</span> + acc.<span class="library" title="Convert a value to a string">str</span>;
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<span class="lineno" id=line13></span> <span class="small_keyword" title="end of extension">end</span>
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</pre></p><p>Of course this doesn't work we get:
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</p><p><pre class="prefmtbg">Attempt1: 0
797-
</pre></p><p>because as we know, the mainline is a coroutine, and it continues on whilst
798-
the <code>adder</code> is sleeping. In the abstract semantics when there is a set
799-
of coroutines waiting to run, the scheduler can run <em>any one</em> of them
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so even without the sleep, it could complete the mainline before completing
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the pipeline.
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</p><pre class='inclusion'>
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examples/ex4.flx</pre>
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<p><pre class='flxbg'><span class="lineno" id=line1></span> <span class="small_keyword" title="end of extension">begin</span>
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<span class="lineno" id=line2></span> <span class="big_keyword" title="Define a mutable variable">var</span> acc = 0;
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<span class="lineno" id=line3></span> chip adder connector io pin inp: %&lt;<span class="library" title="binding of C int type">int</span> {
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<span class="lineno" id=line4></span> <span class="small_keyword" title="while loop">while</span> <span class="library" title="truth value">true</span> <span class="small_keyword" title="imperative code begins">do</span>
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<span class="lineno" id=line5></span> <span class="big_keyword" title="Define a mutable variable">var</span> elt = read io.inp;
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<span class="lineno" id=line6></span> acc = acc + elt;
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<span class="lineno" id=line7></span> <span class="small_keyword" title="end of body">done</span>
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<span class="lineno" id=line8></span> }
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<span class="lineno" id=line9></span>
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<span class="lineno" id=line10></span> run (source_from_list x |-&gt; adder);
814-
<span class="lineno" id=line11></span> <span class="library" title="Print a string to standard output with newline appended">println</span>$ <span class="fstring">"Attempt2: "</span> + acc.<span class="library" title="Convert a value to a string">str</span>;
815-
<span class="lineno" id=line12></span> <span class="small_keyword" title="end of extension">end</span>
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</pre></p></div></div><h1 id='The_concept_of_fibration_h'><img src='/share/src/web/images/minus.gif' id='The concept of fibration' onclick='toggle(this,"The_concept_of_fibration_d")' alt='+'/> 4 The concept of fibration</h1><div id='The_concept_of_fibration_d' style='display:block'>
698+
<p>There is a constraint on Felix coroutines: they have to be procedures.
699+
Functions cannot read and write channels. However there is a way around
700+
this problem: you can use the <code>run</code> subroutine to create an run a new,
701+
nested, scheduler.
702+
</p><p>The <code>run</code> subroutine, being a subroutine, returns when it is finished.
703+
</p><p>Unfortunately there is another constraint on nested schedulers: they cannot
704+
do asynchronous I/O.
705+
</p></div></div><h1 id='The_concept_of_fibration_h'><img src='/share/src/web/images/minus.gif' id='The concept of fibration' onclick='toggle(this,"The_concept_of_fibration_d")' alt='+'/> 4 The concept of fibration</h1><div id='The_concept_of_fibration_d' style='display:block'>
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<p>A <em>coroutine system</em> is a collection of processes called <em>fibres</em>
818707
with these properties:
819708
<ul>
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</p><p>In addition, I/O transfers always result in the reader proceeding,
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to give it a chance to actually fetch the data before the write
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might modify it.
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</p><h2 id='next_h'><img src='/share/src/web/images/minus.gif' id='next' onclick='toggle(this,"next_d")' alt='+'/> 4.1 next</h2><div id='next_d' style='display:block'>
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<p>stuff
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</pre></p><p>stuff
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</p></div></div><h1 id='high_h'><img src='/share/src/web/images/minus.gif' id='high' onclick='toggle(this,"high_d")' alt='+'/> 5 high</h1><div id='high_d' style='display:block'>
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<p>blam
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</p><h2 id='med1_h'><img src='/share/src/web/images/minus.gif' id='med1' onclick='toggle(this,"med1_d")' alt='+'/> 5.1 med1</h2><div id='med1_d' style='display:block'>
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<p>stuff
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</p></div><h2 id='med2_h'><img src='/share/src/web/images/minus.gif' id='med2' onclick='toggle(this,"med2_d")' alt='+'/> 5.2 med2</h2><div id='med2_d' style='display:block'>
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<p>stuff
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</p></div><h2 id='med3_h'><img src='/share/src/web/images/minus.gif' id='med3' onclick='toggle(this,"med3_d")' alt='+'/> 5.3 med3</h2><div id='med3_d' style='display:block'>
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<p>stuff <em>inline html works</em>
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but we have <code>micros</code> for inline code as well.
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<a href= https://www.itkservices2.com/nem_review_1.2>See ITK stuff</a>
926-
</p><h3 id='low_h'><img src='/share/src/web/images/minus.gif' id='low' onclick='toggle(this,"low_d")' alt='+'/> 5.3.1 low</h3><div id='low_d' style='display:block'>
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<p>level 3 stuff
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</p><p><pre class='flxbg'><span class="lineno" id=line1></span> blah
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</pre></p><p>stuff
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</p></div></div></div><!--Main Content Body End-->
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</p></div><!--Main Content Body End-->
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</div> <!-- rightpanel contents end -->
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<hr>

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