Appendix A. Common Functions for Functional Programming in JavaScript

This Appendix covers common functions for functional programming in JavaScript:

• Array Functions:

  var flatten = function(arrays) {
    return arrays.reduce( function(p,n){
      return p.concat(n);
    });
  };
  
  var invert = function(arr) {
    return arr.map(function(x, i, a) {
      return a[a.length - (i+1)];
    });
  };

• Binding Functions:

  var bind = Function.prototype.call.bind(Function.prototype.bind);
  var call = bind(Function.prototype.call, Function.prototype.call);
  var apply = bind(Function.prototype.call, Function.prototype.apply);

• Category Theory:

  var checkTypes = function( typeSafeties ) {
    arrayOf(func)(arr(typeSafeties));
    var argLength = typeSafeties.length;
    return function(args) {
      arr(args);
      if (args.length != argLength) {
        throw new TypeError('Expected '+ argLength + ' arguments');
      }
      var results = [];
      for (var i=0; i<argLength; i++) {
        results[i] = typeSafeties...