Javascript

Functional Aspects

Untested lift from google-goopy. Feel free to fix and add more working examples.

 var parts = partition((function (x) {return ((x % 2) == 0);}),
                       homogenousList);
 var evens = parts[0];
 var odds = parts[1];

 // window.alert("evens = " + evens + " odds = " + odds);

 var res = map((function (x) {return "stringified: " + x;}),
               homogenousList);
 window.alert(res);

 iter(window.alert, homogenousList);

 iter(window.alert, heterogenousMap);

 window.alert(filter((function(x){return ((x%2)==1);}), homogenousList));

functional.js

function some(f, l) {
    for (var x in l) {
        if (f(l[x])) return true;
    }
    return false;
}

function every(f, l) {
    for (var x in l) {
        if (!f(l[x])) return false;
    }
    return true;
}

function find(p, l, start) {
    var z = l.length;
    var s;
    if (arguments < 3) s = 0;
    else s = start;
    for (var i = s; i<z; ++i) {
        if (p(l[i])) return i;
    }
    return -1;
}

/* Single list map functions that don't work with Javascript objects make the
 * baby jesus cry!
 * Question: Does Javascript's for/in loop give you the desired behavior of iterating
 * over the elements of an array? */
function map(f, l) {
    var res = [];
    for (var i in l) {
        res.push(f(l[i]));
    }
    return res;
}

/* Here's a fully general map that even works when f is a method of a specific object
 * instance: */
function map(f, l0) {
    var res = [], args = [];
    for (var j = 0; j < l0.length; j++) {
        for (var i = 1; i < arguments.length; i++) {
            args.push(arguments[i][j]);
        }
        res.push(f.apply(this, args));
        args = [];
    }
    return res;
}

function iter(f, l) {
    for (var i in l) {
        f(l[i]);
    }
}

function fold_left(f, i, l) {
    var a = i;
    for (var i in l) {
        a = f(a, l[i]);
    }
    return a;
}


function fold_right(f, i, l) {
    var a = i;
    var z = l.length-1;
    for (var i=z; i >= 0; --i) {
        a = f(l[i], a);
    }
    return a;
}

// filter(function p, array l)
//
// function p returns a boolean value.  l contains
// the data to be filtered.
//
// the return value is an array containing all the elements
// in l for which p returns true.
function filter(p, l) {
    var res = [];
    for (var i in l) {
        if (p(l[i])) res.push(l[i]);
    }
    return res;
}

// partition(function p, array l)
//
// function p returns a boolean value.  l contains the
// data to be partitioned.
//
// The return value is an array containing two arrays: the first
// are those elements from l for which p returned true, and the second
// are the remainder.
function partition(p, l) {
    var res1 = [];
    var res2 = [];
    for (var i in l) {
        if (p(l[i])) res1.push(l[i]);
        else res2.push(l[i]);
    }
    return [res1, res2];
}

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last updated 2 years ago #