Solution to 99 lisp problems: P08 with functional javascript

Question

Solution to 99 lisp problems: P08, with functional javascript

If a list contains repeated elements they should be replaced with a single copy of the element. The order of the elements should not be changed.

* (compress '(a a a a b c c a a d e e e e))
 (A B C A D E)

Anyone want to review?

function cond( check, _then, _continuation ) {
 if(check) return _then( _continuation )
 else return _continuation()
}
function compress( list ) {
 return (function check( index, item, nextItem, compressed ) {
 return cond( item !== nextItem, function _then( continuation ) {
 compressed = compressed.concat([ item ])
 return continuation()
 },
 function _continueation() {
 return cond(!nextItem, function _then() {
 return compressed
 }, 
 function _continuation() {
 return check( index + 1, list[index + 1], list[index + 2], compressed ) 
 })
 })
 })( 0, list[0], list[1], [] )
}

ref:
http://www.ic.unicamp.br/~meidanis/courses/mc336/2006s2/funcional/L-99_Ninety-Nine_Lisp_Problems.html

• Inkbug: Wouldn't a loop or recursive calling be a better idea?
• Inkbug: The cond function can probably be replaced with a ternary operator and switching the order a little.

Answer 1

I don't think you need so much complexity in javascript. It's not a fully functional language, don't try to make it so.

var arr = [
 'a', 'a', 'a', 'b', 'b', 'c', 'd', 'd', 'a', 'e', 'e', 'e'
];
arr = arr.filter( function( el, i ) {
 // return if the current isn't the same as the next
 return el !== arr[ i + 1 ];
});
console.log( arr ); // ["a", "b", "c", "d", "a", "e"]

This is 2 lines.

• delete me: The function passed to filter can be generalized by adding a third parameter arr.