diff options
Diffstat (limited to 'manuals/sly/Signals.html')
| -rw-r--r-- | manuals/sly/Signals.html | 332 |
1 files changed, 332 insertions, 0 deletions
diff --git a/manuals/sly/Signals.html b/manuals/sly/Signals.html new file mode 100644 index 0000000..b24283b --- /dev/null +++ b/manuals/sly/Signals.html @@ -0,0 +1,332 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 2013, 2014 David Thompson davet@gnu.org + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 +or any later version published by the Free Software Foundation; +with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. +A copy of the license is included in the section entitled "GNU +Free Documentation License". + +A copy of the license is also available from the Free Software +Foundation Web site at http://www.gnu.org/licenses/fdl.html. + + +The document was typeset with +http://www.texinfo.org/ (GNU Texinfo). + --> +<!-- Created by GNU Texinfo 6.0, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Sly: Signals</title> + +<meta name="description" content="Sly: Signals"> +<meta name="keywords" content="Sly: Signals"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta charset="UTF-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Index.html#Index" rel="index" title="Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Time.html#Time" rel="up" title="Time"> +<link href="Coroutines.html#Coroutines" rel="next" title="Coroutines"> +<link href="Time.html#Time" rel="prev" title="Time"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.indentedblock {margin-right: 0em} +blockquote.smallindentedblock {margin-right: 0em; font-size: smaller} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smalllisp {margin-left: 3.2em} +kbd {font-style: oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space: nowrap} +span.nolinebreak {white-space: nowrap} +span.roman {font-family: serif; font-weight: normal} +span.sansserif {font-family: sans-serif; font-weight: normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en"> +<a name="Signals"></a> +<div class="header"> +<p> +Next: <a href="Coroutines.html#Coroutines" accesskey="n" rel="next">Coroutines</a>, Up: <a href="Time.html#Time" accesskey="u" rel="up">Time</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html#Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Signals-1"></a> +<h4 class="subsection">4.3.1 Signals</h4> + +<div class="example"> +<pre class="example">(use-modules (sly signal)) +</pre></div> + +<p>Game state is a function of time. The player’s score, the current +stage, an enemy’s hit points, etc. all change in response to events +that happen at discrete points in time. Typically, this means that a +number of callback procedures are registered to respond to events +which mutate the relevant data structures. However, this approach, +while simple and effective, comes at the price of readability, +reproducibility, and expression. Instead of explicitly mutating data +and entering “callback hell”, Sly abstracts and formalizes the +process using a functional reactive programming style. +</p> +<p>In Sly, time-varying values are called “signals”, and they are +defined in a declarative and functional manner. Rather than +describing the process of mutation procedurally, one describes the +relationships between signals instead. The result is a “signal +graph”, a directed acyclic graph of event responses. +</p> +<div class="example"> +<pre class="example">(define-signal position + (signal-fold v+ (vector2 320 240) + (signal-map (lambda (v) (v* v 4)) + (signal-sample 1 key-arrows)))) +</pre></div> + +<p>This signal describes a relationship between the arrow keys on the +keyboard and the position of the player. <code>signal-sample</code> is used +to trigger a signal update upon every game tick that provides the +current state of the arrow keys. <code>key-arrows</code> is a 2D vector +that maps to the current state of the arrow keys, allowing for 8 +directional movement. This vector is then scaled 4x to make the +player move faster. Finally, the scaled vector is added to the +previous player position via <code>signal-fold</code>. The player’s +position is at (320, 240) initially. As you can see, there are no +callbacks and explicit mutation needed, and the position seems to +magically change with the passage of time. +</p> +<dl> +<dt><a name="index-signal_003f"></a>Scheme Procedure: <strong>signal?</strong> <em><var>obj</var></em></dt> +<dd><p>Return <code>#t</code> if <var>obj</var> is a signal. +</p></dd></dl> + +<dl> +<dt><a name="index-make_002dsignal"></a>Scheme Procedure: <strong>make-signal</strong> <em><var>value</var></em></dt> +<dd><p>Wrap <var>value</var> in a signal. +</p></dd></dl> + +<dl> +<dt><a name="index-define_002dsignal"></a>Scheme Syntax: <strong>define-signal</strong> <em><var>name</var> <var>value</var></em></dt> +<dd><p>Create a top-level signal variable called <var>name</var>. If the variable +already exists and refers to a signal then its outputs will be spliced +into the new signal. If the given value is not a signal then it will +be put into one via <code>make-signal</code>. +</p> +<p><code>define-signal</code> is particularly useful when working at the REPL. +A top-level signal variable defined by <code>define-signal</code> can be +redefined at runtime, and the signals that depended on the old signal +will continue to work with the new signal. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dref"></a>Scheme Procedure: <strong>signal-ref</strong> <em><var>signal</var></em></dt> +<dd><p>Return the value stored within <var>signal</var>. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dref_002dmaybe"></a>Scheme Procedure: <strong>signal-ref-maybe</strong> <em>object</em></dt> +<dd><p>Return the value stored within <var>object</var> if <var>object</var> is a +signal. Otherwise, return <var>object</var>. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dlet"></a>Scheme Syntax: <strong>signal-let</strong> <em>((<var>var</var> <var>signal</var>) …) <var>body</var> …</em></dt> +<dd><p>Evaluate <var>body</var> in the context of the local bindings defined by +the two-element lists <code>((var signal) …)</code>. +<code>signal-let</code> works like regular <code>let</code>, except that it +derefences <var>signal</var> before binding to <var>var</var>. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dlet_002a"></a>Scheme Syntax: <strong>signal-let*</strong> <em>((<var>var</var> <var>signal</var>) …) <var>body</var> …</em></dt> +<dd><p>Similar to <code>signal-let</code>, but the variable bindings are performed +sequentially. This means that all initialization expressions are +allowed to use the variables defined to the their left in the binding +list. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dset_0021"></a>Scheme Procedure: <strong>signal-set!</strong> <em>signal-box value</em></dt> +<dd><p>Change the contents of <var>signal</var> to <var>value</var>. This procedure +should almost never be used, except to bootstrap a root node of a +signal graph. +</p></dd></dl> + +<dl> +<dt><a name="index-hook_002d_003esignal"></a>Scheme Procedure: <strong>hook->signal</strong> <em><var>hook</var> <var>init</var> <var>proc</var></em></dt> +<dd><p>Create a new signal whose initial value is <var>init</var> and whose future +values are calculated by applying <var>proc</var> to the arguments passed +when <var>hook</var> is run. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dmerge"></a>Scheme Procedure: <strong>signal-merge</strong> <em><var>signal1</var> <var>signal2</var> . <var>rest</var></em></dt> +<dd><p>Create a new signal whose value is the that of the most recently +updated signal in <var>signal1</var>, <var>signal2</var>, etc. The initial +value is that of <var>signal1</var>. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dzip"></a>Scheme Procedure: <strong>signal-zip</strong> <em>. <var>signals</var></em></dt> +<dd><p>Create a new signal whose value is a list of the values stored in +<var>signals</var>. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dmap"></a>Scheme Procedure: <strong>signal-map</strong> <em><var>proc</var> <var>signal</var> . <var>rest</var></em></dt> +<dd><p>Create a new signal that applies <var>proc</var> to the values of +<var>SIGNAL</var>. More than one input signal may be specified, in which +case <var>proc</var> must accept as many arguments as there are input +signals. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dsample_002don"></a>Scheme Procedure: <strong>signal-sample-on</strong> <em><var>value-signal</var> <var>sample-signal</var></em></dt> +<dd><p>Create a new signal that takes on the value of <var>value-signal</var> +whenever <var>sample-signal</var> receives a new value. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dnegate"></a>Scheme Procedure: <strong>signal-negate</strong> <em><var>signal</var></em></dt> +<dd><p>Create a new signal whose value is the negation of <var>signal</var> by +applying <code>not</code> to each value received. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dfold"></a>Scheme Procedure: <strong>signal-fold</strong> <em><var>proc</var> <var>init</var> <var>signal</var> . <var>rest</var></em></dt> +<dd><p>Create a new signal that applies <var>proc</var> with the value received +from <var>signal</var> and the past value of itself, starting with +<var>init</var>. Like <code>signal-map</code>, more than one input signal may be +given. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dfilter"></a>Scheme Procedure: <strong>signal-filter</strong> <em><var>predicate</var> <var>default</var> <var>signal</var></em></dt> +<dd><p>Create a new signal that takes on the value received from <var>signal</var> +when it satisfies the procedure <var>predicate</var>. The value of the +signal is <var>default</var> in the case that the predicate is never +satisfied. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002ddrop"></a>Scheme Procedure: <strong>signal-drop</strong> <em><var>predicate</var> <var>default</var> <var>signal</var></em></dt> +<dd><p>Create a new signal that takes on the value received from <var>signal</var> +when it does <em>not</em> satisfy the procedure <var>predicate</var>. The +value of the signal is <var>default</var> in the case that the predicate is +never satisfied. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002ddrop_002drepeats"></a>Scheme Procedure: <strong>signal-drop-repeats</strong> <em><var>signal</var> [<var>equal?</var>]</em></dt> +<dd><p>Create a new signal that drops the value received from <var>signal</var> +when it is equivalent to the current value. By default, <code>equal?</code> +is used for testing equivalence. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dswitch"></a>Scheme Procedure: <strong>signal-switch</strong> <em><var>predicate</var> <var>on</var> <var>off</var></em></dt> +<dd><p>Create a new signal whose value is that of the signal <var>on</var> when +the signal <var>predicate</var> is true, or the value of the signal +<var>off</var> otherwise. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dconstant"></a>Scheme Procedure: <strong>signal-constant</strong> <em><var>constant</var> <var>signal</var></em></dt> +<dd><p>Create a new signal whose value is always <var>constant</var> no matter the +value received from <var>signal</var>. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dcount"></a>Scheme Procedure: <strong>signal-count</strong> <em><var>signal</var> [<var>start</var>] [<var>step</var>]</em></dt> +<dd><p>Create a new signal that increments a counter by <var>step</var> when a +value from <var>signal</var> is received, starting from <var>start</var>. By +default, <var>start</var> is 0 and <var>step</var> is 1. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dtap"></a>Scheme Procedure: <strong>signal-tap</strong> <em><var>proc</var> <var>signal</var></em></dt> +<dd><p>Create a new signal that applies <var>proc</var> for side-effects when a +value from <var>signal</var> is received. The value of the new signal will +always be the value of <var>signal</var>. This signal is a convenient way +to sneak in a procedure that with a side-effect into a signal graph. +Such a signal might write text to a file, or play a sound. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dtimestamp"></a>Scheme Procedure: <strong>signal-timestamp</strong> <em><var>signal</var></em></dt> +<dd><p>Create a new signal whose value is a pair, the car of which is the +time that the value of <var>signal</var> was received and the cdr of which +is the received value. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dtime"></a>Scheme Procedure: <strong>signal-time</strong> <em><var>signal</var></em></dt> +<dd><p>Create a new signal whose value is the time that the value of +<var>signal</var> was received. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dsample"></a>Scheme Procedure: <strong>signal-sample</strong> <em><var>step</var> <var>signal</var></em></dt> +<dd><p>Create a new signal that takes on the value of <var>signal</var> every +<var>step</var> ticks. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002devery"></a>Scheme Procedure: <strong>signal-every</strong> <em><var>step</var></em></dt> +<dd><p>Create a new signal that emits <var>step</var> every <var>step</var> ticks. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dsince"></a>Scheme Procedure: <strong>signal-since</strong> <em><var>step</var> <var>signal</var></em></dt> +<dd><p>Create a new signal that emits the time since <var>signal</var> was updated +ever <var>step</var> ticks. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002ddelay"></a>Scheme Procedure: <strong>signal-delay</strong> <em><var>delay</var> <var>signal</var></em></dt> +<dd><p>Create a new signal that delays propagation of <var>signal</var> by +<var>delay</var> ticks.. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dthrottle"></a>Scheme Procedure: <strong>signal-throttle</strong> <em>delay signal</em></dt> +<dd><p>Create a new signal that propagates <var>signal</var> at most once every +<var>delay</var> ticks. +</p></dd></dl> + +<dl> +<dt><a name="index-signal_002dgenerator"></a>Scheme Syntax: <strong>signal-generator</strong> <em><var>body</var> …</em></dt> +<dd><p>Create a new signal whose value is the most recently yielded value of +the coroutine defined by <var>body</var>. A special <code>yield</code> syntax is +available within <var>body</var> to specify which values are passed to the +signal. +</p></dd></dl> + +<hr> +<div class="header"> +<p> +Next: <a href="Coroutines.html#Coroutines" accesskey="n" rel="next">Coroutines</a>, Up: <a href="Time.html#Time" accesskey="u" rel="up">Time</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html#Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |