"Bryan Hayes (Hayes Technologies)" wrote:
I am totally new to Haskell, so maybe this is a stupid question. Various languages have pointers (or references), for good reason. Haskell can at least partly do without them (they are only existing internally somehow). My question is: Does Haskell principally not need pointers (i.e. in case of 2 data structures needing to reference an other very large data structure) or is this a design flaw or have a overlooked something?
All Haskell compilers use pointers internally. The idea is that because Haskell is referentially transparent and side effect free, you can overwrite a function application with its result. For example, let x = [1..1000] in foo (A x) (B x) Will internally have "x" pointing to the function application [1..1000], when this function application is evaluated it will overwrite the memory cell "x" points to with the result. So eventually it will look like this: +---+---+ +---+---+ | A | x | | B | x | +---+---+ +---+---+ | | +---+-------+ | V +---+---+------+ | : | 1 | tail |---> The list 2..1000 +---+---+------+ Where each block is a memory cell and each arrow is a pointer. A book that describes this a lot better is: Simon Peyton-Jones. The implementation of functional programming languages. Prentice-Hall, 1987 Jan