Generator/lazy sequence class for JavaScript

generator_compact.js

function Generator(f,s,i){i=0;return{first:function(){return s[i=0];},next:function(){return s.length<=++i?s[i]=f(s):s[i];},nth:function(n){while(s.length<=n)this.next();return s[n];},take:function(n){this.nth(n);return s.slice(0,n);}};}

generator_full.js

function Generator ( fn , state) {

  var i = 0;

  return {
    first: function() {
      i = 0;
      return state[ i ];
    },
    next: function() {
      i = i + 1;
      if ( typeof( state[ i ] ) === "undefined" ) {
            
        state[ i ] = fn( state );

      }
      return state[ i ];
    },
    nth: function( n ) {
      while ( typeof( state[ n ] ) === "undefined" ) {
        this.next();
      }
      return state[ n ];
    },
    take: function( n ) {
      // Ensure that the nth element has been generated
      this.nth( n );
      return state.slice( 0 , n );
    }
  };
};

var integers = new Generator(function ( state ) {
                               
                               return state[ state.length - 1 ] + 1;

                             }), [ 1 ]);

var fib = new Generator(function ( state ) {
                               
                               return state[ state.length - 2 ] + state[ state.length - 1 ];

                             }), [ 1 , 1 ]);

var factorials = new Generator(function ( state ) {
                               
                               return state[ state.length - 1 ] * ( state.length + 1 ) ];

                             }), [ 1 ]);