source: Dev/trunk/src/client/dojox/lang/functional/lambda.js @ 532

define(["../..", "dojo/_base/lang", "dojo/_base/array"], function(dojox, lang, arr){
        var df = lang.getObject("lang.functional", true, dojox);

// This module adds high-level functions and related constructs:
//      - anonymous functions built from the string

// Acknowledgements:
//      - lambda() is based on work by Oliver Steele
//              (http://osteele.com/sources/javascript/functional/functional.js)
//              which was published under MIT License

// Notes:
//      - lambda() produces functions, which after the compilation step are
//              as fast as regular JS functions (at least theoretically).

// Lambda input values:
//      - returns functions unchanged
//      - converts strings to functions
//      - converts arrays to a functional composition

        var lcache = {};

        // split() is augmented on IE6 to ensure the uniform behavior
        var split = "ab".split(/a*/).length > 1 ? String.prototype.split :
                        function(sep){
                                 var r = this.split.call(this, sep),
                                         m = sep.exec(this);
                                 if(m && m.index == 0){ r.unshift(""); }
                                 return r;
                        };
                        
        var lambda = function(/*String*/ s){
                var args = [], sects = split.call(s, /\s*->\s*/m);
                if(sects.length > 1){
                        while(sects.length){
                                s = sects.pop();
                                args = sects.pop().split(/\s*,\s*|\s+/m);
                                if(sects.length){ sects.push("(function(" + args.join(", ") + "){ return (" + s + "); })"); }
                        }
                }else if(s.match(/\b_\b/)){
                        args = ["_"];
                }else{
                        var l = s.match(/^\s*(?:[+*\/%&|\^\.=<>]|!=)/m),
                                r = s.match(/[+\-*\/%&|\^\.=<>!]\s*$/m);
                        if(l || r){
                                if(l){
                                        args.push("$1");
                                        s = "$1" + s;
                                }
                                if(r){
                                        args.push("$2");
                                        s = s + "$2";
                                }
                        }else{
                                // the point of the long regex below is to exclude all well-known
                                // lower-case words from the list of potential arguments
                                var vars = s.
                                        replace(/(?:\b[A-Z]|\.[a-zA-Z_$])[a-zA-Z_$\d]*|[a-zA-Z_$][a-zA-Z_$\d]*:|this|true|false|null|undefined|typeof|instanceof|in|delete|new|void|arguments|decodeURI|decodeURIComponent|encodeURI|encodeURIComponent|escape|eval|isFinite|isNaN|parseFloat|parseInt|unescape|dojo|dijit|dojox|window|document|'(?:[^'\\]|\\.)*'|"(?:[^"\\]|\\.)*"/g, "").
                                        match(/([a-z_$][a-z_$\d]*)/gi) || [], t = {};
                                arr.forEach(vars, function(v){
                                        if(!t.hasOwnProperty(v)){
                                                args.push(v);
                                                t[v] = 1;
                                        }
                                });
                        }
                }
                return {args: args, body: s};   // Object
        };

        var compose = function(/*Array*/ a){
                return a.length ?
                                        function(){
                                                var i = a.length - 1, x = df.lambda(a[i]).apply(this, arguments);
                                                for(--i; i >= 0; --i){ x = df.lambda(a[i]).call(this, x); }
                                                return x;
                                        }
                                :
                                        // identity
                                        function(x){ return x; };
        };

        lang.mixin(df, {
                // lambda
                rawLambda: function(/*String*/ s){
                        // summary:
                        //              builds a function from a snippet, or array (composing),
                        //              returns an object describing the function; functions are
                        //              passed through unmodified.
                        // description:
                        //              This method is to normalize a functional representation (a
                        //              text snippet) to an object that contains an array of
                        //              arguments, and a body , which is used to calculate the
                        //              returning value.
                        return lambda(s);       // Object
                },
                buildLambda: function(/*String*/ s){
                        // summary:
                        //              builds a function from a snippet, returns a string, which
                        //              represents the function.
                        // description:
                        //              This method returns a textual representation of a function
                        //              built from the snippet. It is meant to be evaled in the
                        //              proper context, so local variables can be pulled from the
                        //              environment.
                        var l = lambda(s);
                        return "function(" + l.args.join(",") + "){return (" + l.body + ");}";  // String
                },
                lambda: function(/*Function|String|Array*/ s){
                        // summary:
                        //              builds a function from a snippet, or array (composing),
                        //              returns a function object; functions are passed through
                        //              unmodified.
                        // description:
                        //              This method is used to normalize a functional
                        //              representation (a text snippet, an array, or a function) to
                        //              a function object.
                        if(typeof s == "function"){ return s; }
                        if(s instanceof Array){ return compose(s); }
                        if(lcache.hasOwnProperty(s)){ return lcache[s]; }
                        var l = lambda(s);
                        return lcache[s] = new Function(l.args, "return (" + l.body + ");");    // Function
                },
                clearLambdaCache: function(){
                        // summary:
                        //              clears internal cache of lambdas
                        lcache = {};
                }
        });
        
        return df;
});