- Author:
- David Nickerson <nickerso@users.sourceforge.net>
- Date:
- 2009-07-16 02:00:03+12:00
- Desc:
- the starting point for the HH tutorial example
- Permanent Source URI:
- https://models.fieldml.org/workspace/a1/rawfile/f6a8f90307388eb4b040ee3566b84d88b59247f7/dojo-presentation/js/dojo/dojox/lang/functional/numrec.js
dojo.provide("dojox.lang.functional.numrec");
dojo.require("dojox.lang.functional.lambda");
dojo.require("dojox.lang.functional.util");
// This module provides recursion combinators:
// - a simplified numeric linear recursion combinator.
// Acknoledgements:
// - recursion combinators are inspired by Manfred von Thun's article
// "Recursion Theory and Joy"
// (http://www.latrobe.edu.au/philosophy/phimvt/joy/j05cmp.html)
// Notes:
// - recursion combinators produce a function, which implements
// their respective recusion patterns. String lambdas are inlined, if possible.
(function(){
var df = dojox.lang.functional, inline = df.inlineLambda,
_r_i = ["_r", "_i"];
df.numrec = function(/*Object*/ then, /*Function|String|Array*/ after){
// summary:
// Generates a function for the simplified numeric linear recursion pattern.
// All parameter functions are called in the context of "this" object.
// description:
// This is a simplification of the linear recursion combinator:
// - the generated function takes one numeric parameter "x",
// - the "cond" is fixed and checks for 0.
// - the "before" is fixed and the generated function is called with "x - 1".
// - the "above is called with two parameters: the return from the generated
// function, and with "x".
// - as you can see the recursion is done by decreasing the parameter,
// and calling itself until it reaches 0.
// then:
// The value, which is used upon termination of the recursion.
// It will be returned as the value of the generated function.
// above:
// The lambda expression, which is called after the recursive step.
// It accepts two parameters: the returned value from the recursive step, and
// the original parameter. The returned value will be returned as the value of
// the generated function.
var a, as, dict = {},
add2dict = function(x){ dict[x] = 1; };
if(typeof after == "string"){
as = inline(after, _r_i, add2dict);
}else{
a = df.lambda(after);
as = "_a.call(this, _r, _i)";
}
var locals = df.keys(dict),
f = new Function(["_x"], "var _t=arguments.callee,_r=_t.t,_i".concat( // Function
locals.length ? "," + locals.join(",") : "",
a ? ",_a=_t.a" : "",
";for(_i=1;_i<=_x;++_i){_r=",
as,
"}return _r"
));
f.t = then;
if(a){ f.a = a; }
return f;
};
})();
/*
For documentation only:
1) The original recursive version:
var numrec1 = function(then, after){
var after = df.lambda(after);
return function(x){
return x ? after.call(this, arguments.callee.call(this, x - 1), x) : then;
};
};
2) The original iterative version (before minification and inlining):
var numrec2 = function(then, after){
var after = df.lambda(after);
return function(x){
var ret = then, i;
for(i = 1; i <= x; ++i){
ret = after.call(this, ret, i);
}
return ret;
};
};
*/
