From 9224412274e1e1a31a959083bb257a7d6ab2b113 Mon Sep 17 00:00:00 2001 From: David Thompson Date: Fri, 19 Aug 2016 20:40:12 -0400 Subject: Add Sly manual. --- manuals/sly/Signals.html | 332 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 332 insertions(+) create mode 100644 manuals/sly/Signals.html (limited to 'manuals/sly/Signals.html') 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 @@ + + + + + +Sly: Signals + + + + + + + + + + + + + + + + + + + + +
+

+Next: , Up: Time   [Contents][Index]

+
+
+ +

4.3.1 Signals

+ +
+
(use-modules (sly signal))
+
+ +

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. +

+

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. +

+
+
(define-signal position
+  (signal-fold v+ (vector2 320 240)
+               (signal-map (lambda (v) (v* v 4))
+                           (signal-sample 1 key-arrows))))
+
+ +

This signal describes a relationship between the arrow keys on the +keyboard and the position of the player. signal-sample is used +to trigger a signal update upon every game tick that provides the +current state of the arrow keys. key-arrows 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 signal-fold. 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. +

+
+
Scheme Procedure: signal? obj
+

Return #t if obj is a signal. +

+ +
+
Scheme Procedure: make-signal value
+

Wrap value in a signal. +

+ +
+
Scheme Syntax: define-signal name value
+

Create a top-level signal variable called name. 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 make-signal. +

+

define-signal is particularly useful when working at the REPL. +A top-level signal variable defined by define-signal can be +redefined at runtime, and the signals that depended on the old signal +will continue to work with the new signal. +

+ +
+
Scheme Procedure: signal-ref signal
+

Return the value stored within signal. +

+ +
+
Scheme Procedure: signal-ref-maybe object
+

Return the value stored within object if object is a +signal. Otherwise, return object. +

+ +
+
Scheme Syntax: signal-let ((var signal) …) body …
+

Evaluate body in the context of the local bindings defined by +the two-element lists ((var signal) …). +signal-let works like regular let, except that it +derefences signal before binding to var. +

+ +
+
Scheme Syntax: signal-let* ((var signal) …) body …
+

Similar to signal-let, 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. +

+ +
+
Scheme Procedure: signal-set! signal-box value
+

Change the contents of signal to value. This procedure +should almost never be used, except to bootstrap a root node of a +signal graph. +

+ +
+
Scheme Procedure: hook->signal hook init proc
+

Create a new signal whose initial value is init and whose future +values are calculated by applying proc to the arguments passed +when hook is run. +

+ +
+
Scheme Procedure: signal-merge signal1 signal2 . rest
+

Create a new signal whose value is the that of the most recently +updated signal in signal1, signal2, etc. The initial +value is that of signal1. +

+ +
+
Scheme Procedure: signal-zip . signals
+

Create a new signal whose value is a list of the values stored in +signals. +

+ +
+
Scheme Procedure: signal-map proc signal . rest
+

Create a new signal that applies proc to the values of +SIGNAL. More than one input signal may be specified, in which +case proc must accept as many arguments as there are input +signals. +

+ +
+
Scheme Procedure: signal-sample-on value-signal sample-signal
+

Create a new signal that takes on the value of value-signal +whenever sample-signal receives a new value. +

+ +
+
Scheme Procedure: signal-negate signal
+

Create a new signal whose value is the negation of signal by +applying not to each value received. +

+ +
+
Scheme Procedure: signal-fold proc init signal . rest
+

Create a new signal that applies proc with the value received +from signal and the past value of itself, starting with +init. Like signal-map, more than one input signal may be +given. +

+ +
+
Scheme Procedure: signal-filter predicate default signal
+

Create a new signal that takes on the value received from signal +when it satisfies the procedure predicate. The value of the +signal is default in the case that the predicate is never +satisfied. +

+ +
+
Scheme Procedure: signal-drop predicate default signal
+

Create a new signal that takes on the value received from signal +when it does not satisfy the procedure predicate. The +value of the signal is default in the case that the predicate is +never satisfied. +

+ +
+
Scheme Procedure: signal-drop-repeats signal [equal?]
+

Create a new signal that drops the value received from signal +when it is equivalent to the current value. By default, equal? +is used for testing equivalence. +

+ +
+
Scheme Procedure: signal-switch predicate on off
+

Create a new signal whose value is that of the signal on when +the signal predicate is true, or the value of the signal +off otherwise. +

+ +
+
Scheme Procedure: signal-constant constant signal
+

Create a new signal whose value is always constant no matter the +value received from signal. +

+ +
+
Scheme Procedure: signal-count signal [start] [step]
+

Create a new signal that increments a counter by step when a +value from signal is received, starting from start. By +default, start is 0 and step is 1. +

+ +
+
Scheme Procedure: signal-tap proc signal
+

Create a new signal that applies proc for side-effects when a +value from signal is received. The value of the new signal will +always be the value of signal. 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. +

+ +
+
Scheme Procedure: signal-timestamp signal
+

Create a new signal whose value is a pair, the car of which is the +time that the value of signal was received and the cdr of which +is the received value. +

+ +
+
Scheme Procedure: signal-time signal
+

Create a new signal whose value is the time that the value of +signal was received. +

+ +
+
Scheme Procedure: signal-sample step signal
+

Create a new signal that takes on the value of signal every +step ticks. +

+ +
+
Scheme Procedure: signal-every step
+

Create a new signal that emits step every step ticks. +

+ +
+
Scheme Procedure: signal-since step signal
+

Create a new signal that emits the time since signal was updated +ever step ticks. +

+ +
+
Scheme Procedure: signal-delay delay signal
+

Create a new signal that delays propagation of signal by +delay ticks.. +

+ +
+
Scheme Procedure: signal-throttle delay signal
+

Create a new signal that propagates signal at most once every +delay ticks. +

+ +
+
Scheme Syntax: signal-generator body …
+

Create a new signal whose value is the most recently yielded value of +the coroutine defined by body. A special yield syntax is +available within body to specify which values are passed to the +signal. +

+ +
+
+

+Next: , Up: Time   [Contents][Index]

+
+ + + + + -- cgit v1.2.3