JSWorld API

Summary
=======

Reactive World-style programming in Javascript.



Example
========

Here's a simple program that displays a clickable button.  When the
run() function is called, a button and a red number will be written to
the document; clicking the button will cause the displayed number to
be incremented.  (examples/simple-button.html)

      var jsworld = plt.Jsworld;

      var init_world = 0;

      // press: world -> world
      function press(w) {
          return w + 1;
      }

      function draw(w) {
          return [document.body,
                  [jsworld.p({id: "myPara"}), [jsworld.text(w)]],
                  [jsworld.button(press),
                   [jsworld.text("Press me to increment " + w)]]];
      }
      
      function draw_css(world) {
        return [["myPara", ["color", "red"],
                           ["font-size", "50px"]]];
      }

      function run() {
          jsworld.big_bang(window.document.body, 
                           init_world, 
		           [jsworld.on_draw(draw, draw_css)]);
      }




Types
=====

The main functions passed to an on_draw expect the following types:


dom-sexp: [node, dom-sexp...]

css-sexp: [[string-or-node [string string]...]...]
          


The node-producing functions are described later in this document.
Examples of nodes are:

    var n1 = plt.jsworld.div();
    var n2 = plt.jsworld.p();
    var n3 = plt.jsworld.text("I am a text");

Examples of dom-exps are:

    var dom1 = [n1];
    var dom2 = [n1, [n2, [n3]]]
    var dom3 = [n1, [n2, [n3],
                         [n3]]]


Examples of css-sexps are

    var emptyStyle = [];
    var style1 = [["someNodeId", ["width", "30px"],
                                 ["height", "30px"]]];


big-bang
========

plt.Jsworld.big_bang: node world (listof handler) (listof css-style) -> world

Starts a reactive computation.  If a big_bang is already in effect,
temporarily pauses that computation and begins a new nested one.




Helpers
=======

plt.Jsworld.node_to_tree: node -> dom-sexp

Given a node, produces an dom-sexp of that node.  Useful when you
want to use the existing dom tree in a static HTML file in a big-bang.
See examples/static-with-jsworld for an example of this.





Handler functions
==================
plt.Jsworld.on_draw: (world -> dom-sexp) (world -> (sexpof css-style)) -> handler

Called whenever the world changes; the first argument produces a new
dom, and the second produces the new styles applied to that dom.

Example:

    function draw(w) {
        return [plt.Jsworld.p([["id" "my-para"]]),
                [plt.Jsworld.text("hello world")]
                [plt.Jsworld.text("This is a test")]];
    }

    function draw_css(w) {
        return [["my-para", ["font-size" "large"]]];
    }

    plt.Jsworld.big_bang(...,
                         [... 
                          plt.Jsworld.on_draw(draw, draw_css),
                          ...])


----------------------------------------------------------------------


plt.on_tick: number (world -> world) -> handler

Called after n milliseconds to go from one world to the next.


----------------------------------------------------------------------

plt.stop_when: (world -> boolean) (world -> void) -> handler

Registers a stop-when handler that consumes a world judger.  If the
judge says that th world is stopped, then the reactive computation
completes and the final world value is sent to the second function.


----------------------------------------------------------------------

plt.on_world_change: (world -> void) -> handler

Registers an on-world-chnage handler that listens whenever the world
changes.  The listener must not have an effect on the world.


----------------------------------------------------------------------



Node types
==========

----------------------------------------------------------------------


plt.Jsworld.p: assoc -> node

Creates a P paragraph element.


----------------------------------------------------------------------

plt.Jsworld.div: assoc -> node

Creates a DIV element.


----------------------------------------------------------------------


plt.Jsworld.button: (world -> world) assoc -> node

Creates a BUTTON element; the callback consumes a world and produces
an updated world.


Example:

     plt.Jsworld.button(function(w) { return w + 1; })

produces a button that, when pressed, increments the world by one.

----------------------------------------------------------------------



plt.Jsworld.bidirectional_input: string (world -> string) (world string -> world) assoc -> node

Consumes the types of an element, a function for getting the input's
value from the world, and an updating function that takes the content
of the form to update the world.

Example:

    var node = plt.Jsworld.input("text",
                                 function(w) { return "I see: " + w }
		                 function(w, str) { return w; })

produces an input text field that shows a string representation of the
world, and resists when the user tries to edit the element.


----------------------------------------------------------------------

plt.Jsworld.text: string assoc -> node

Example:

    var node = plt.Jsworld.text("Hello World!")

----------------------------------------------------------------------

plt.Jsworld.h1: string assoc -> node

H1 header.

Example:

    var node = plt.Jsworld.h1("I am a header!")


----------------------------------------------------------------------

plt.Jsworld.img: string assoc -> node

Image.  Consumes the source and produces an image node.

Example:

    var node = plt.Jsworld.img("http://plt-scheme.org/logo.png");