I assume you're talking about lists with mutable pointers. I don't think that's what they're talking about here. Functional (persistent) lists are immutable. You can add elements only by creating a new data structure, similar to a linked list node, that will hold immutable references to the existing list and the new element. By convention the element is considered to be in front of the list. Hence prepending is rather easy (constant time) while appending requires rebuilding the whole list (linear time).
I assume you're talking about lists with mutable pointers. I don't think that's what they're talking about here. Functional (persistent) lists are immutable. [...] Hence prepending is rather easy (constant time) while appending requires rebuilding the whole list (linear time).
You can append in O(1) time using difference lists. They don't have all the niceties of Prolog difference lists, but they are still great if you only have to append:
Comments
Lists don't have O(n) complexity of appending an element, if you keep track of the tail element.
I assume you're talking about lists with mutable pointers. I don't think that's what they're talking about here. Functional (persistent) lists are immutable. You can add elements only by creating a new data structure, similar to a linked list node, that will hold immutable references to the existing list and the new element. By convention the element is considered to be in front of the list. Hence prepending is rather easy (constant time) while appending requires rebuilding the whole list (linear time).
I assume you're talking about lists with mutable pointers. I don't think that's what they're talking about here. Functional (persistent) lists are immutable. [...] Hence prepending is rather easy (constant time) while appending requires rebuilding the whole list (linear time).
You can append in O(1) time using difference lists. They don't have all the niceties of Prolog difference lists, but they are still great if you only have to append:
http://hackage.haskell.org/package/dlist