List implementation in Javascript- ES6 and ES5

The ability to make functions behave like data is one of the most fascinating aspects of functional programming.

This an implementation of classic LISP-style non-mutable lists using the CONS, CAR and CDR functions which have been defined for JS at the top of the files.

Classic Lists are created by nesting calls i.e: (1,2,3,4) => list(1,list(2,list(3,list(4,null)));

As a syntactic sugar a function list_from_seq() has been provided where the list will be created from the arguments directly.

e.g: list_from_seq(1,2,3,4) is equivalent to:

list(1,list(2,list(3,list(4,null)));

Another helper function ltos() has been provided to convert a list to a string.

The primary purpose is to study the data abstraction techniques using functions. The ES6 version demonstrates the power of lambdas.

These functions use recursion ( all of them use tail-recursive versions except for qSort()) and hence if the environment does not support tail-recursion optimization they may blow the stack.

ES6 list_es6 need to be run on environments that support lambdas. These have bee tested on FireFox 33.

list_test is common from both list_es5 and list_es6 and uses plain old JS.

Usage

1. list(head, tail)
   where head is an element tail is a list. if tail == null then that is the end of the list

   syntactic liberty-- if the caller doesn;t provied "tail" it will default to null

   So list(1) and list (1,null) are the same -- a list with 1 member

2. ltos(l)=> list to string

3. reverse(l) -self explanatory

4. append(l,elem) -- a new list created by appending elem to l

5. map(l, mapfn) a new list consisting of elements tranformed using the function mapfn see test_map() in list_test for usage.

6. reduce(l, reduceFn)

   • similar to Array.reduce see test_reduce() in list_test

7. filter(l, filterFn) returns a list consisting of those elements for which the filterFn returns true see filter_test() in test_list.js ffor usage.

8. length(l) - returns the length of l

9. concat(l1,l2)

• returns a list that is the result of concatenation of l1 and l2

7. insertAt(l,at)

• a new list that is the result of inserting an element at position ( at=> 0,1,2....) in l; 8, removeAt(1,at) returns a new list after the renoving the element at the position specified by the second argument.

9. qSort(l)

• quickSort-- returns a sorted version of l using quicksort

Developing

Tools

Created using Eclipse