Pointers in Haskell??

[Jeff Dalton]

> 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.

What does it mean to have a letter ("A", "x", or a number or "tail",
etc) inside a box?

> A book that describes this a lot better is:
> 
>     Simon Peyton-Jones. The implementation of functional
>     programming languages. Prentice-Hall, 1987

Are they always implemented that way these days?

-- J