- 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/linrec.js
dojo.provide("dojox.lang.functional.linrec");
dojo.require("dojox.lang.functional.lambda");
dojo.require("dojox.lang.functional.util");
// This module provides recursion combinators:
// - a 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,
_x ="_x", _r_y_a = ["_r", "_y.a"];
df.linrec = function(
/*Function|String|Array*/ cond,
/*Function|String|Array*/ then,
/*Function|String|Array*/ before,
/*Function|String|Array*/ after){
// summary:
// Generates a function for the linear recursion pattern.
// All parameter functions are called in the context of "this" object.
// cond:
// The lambda expression, which is used to detect the termination of recursion.
// It accepts the same parameter as the generated recursive function itself.
// This function should return "true", if the recursion should be stopped,
// and the "then" part should be executed. Otherwise the recursion will proceed.
// then:
// The lambda expression, which is called upon termination of the recursion.
// It accepts the same parameters as the generated recursive function itself.
// The returned value will be returned as the value of the generated function.
// before:
// The lambda expression, which is called before the recursive step.
// It accepts the same parameter as the generated recursive function itself.
// The returned value should be an array, which is used to call
// the generated function recursively.
// 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 array of parameters used with all other functions.
// The returned value will be returned as the value of the generated function.
var c, t, b, a, cs, ts, bs, as, dict1 = {}, dict2 = {},
add2dict = function(x){ dict1[x] = 1; };
if(typeof cond == "string"){
cs = inline(cond, _x, add2dict);
}else{
c = df.lambda(cond);
cs = "_c.apply(this, _x)";
dict2["_c=_t.c"] = 1;
}
if(typeof then == "string"){
ts = inline(then, _x, add2dict);
}else{
t = df.lambda(then);
ts = "_t.t.apply(this, _x)";
}
if(typeof before == "string"){
bs = inline(before, _x, add2dict);
}else{
b = df.lambda(before);
bs = "_b.apply(this, _x)";
dict2["_b=_t.b"] = 1;
}
if(typeof after == "string"){
as = inline(after, _r_y_a, add2dict);
}else{
a = df.lambda(after);
as = "_a.call(this, _r, _y.a)";
dict2["_a=_t.a"] = 1;
}
var locals1 = df.keys(dict1), locals2 = df.keys(dict2),
f = new Function([], "var _x=arguments,_y,_r".concat( // Function
locals1.length ? "," + locals1.join(",") : "",
locals2.length ? ",_t=_x.callee," + locals2.join(",") : t ? ",_t=_x.callee" : "",
";for(;!",
cs,
";_x=",
bs,
"){_y={p:_y,a:_x}}_r=",
ts,
";for(;_y;_y=_y.p){_r=",
as,
"}return _r"
));
if(c){ f.c = c; }
if(t){ f.t = t; }
if(b){ f.b = b; }
if(a){ f.a = a; }
return f;
};
})();
/*
For documentation only:
1) The original recursive version:
var linrec1 = function(cond, then, before, after){
var cond = df.lambda(cond),
then = df.lambda(then),
before = df.lambda(before),
after = df.lambda(after);
return function(){
if(cond.apply(this, arguments)){
return then.apply(this, arguments);
}
var args = before.apply(this, arguments);
var ret = arguments.callee.apply(this, args);
return after.call(this, ret, arguments);
};
};
2) The original iterative version (before minification and inlining):
var linrec2 = function(cond, then, before, after){
var cond = df.lambda(cond),
then = df.lambda(then),
before = df.lambda(before),
after = df.lambda(after);
return function(){
var args = arguments, top, ret;
// 1st part
for(; !cond.apply(this, args); args = before.apply(this, args)){
top = {prev: top, args: args};
}
ret = then.apply(this, args);
//2nd part
for(; top; top = top.prev){
ret = after.call(this, ret, top.args);
}
return ret;
};
};
*/
