Re: [Caml-list] Re: Parameter evaluation order

[Fernando Alegre <fernando@cc.gatech.edu>]

On Fri, Aug 26, 2005 at 03:36:31PM +0300, Ville-Pertti Keinonen wrote:

> Consider an explicit implementation of lists:
> 
> type 'a list = Cons of 'a * 'a list | Nil
> 
> Now, you'd write the list [ a; b; c; d ] (where a, b, c and d could be 
> complex expressions) as
> 
> Cons (a, Cons (b, Cons (c, (Cons (d, Nil)))))
> 
> You need to have Cons (d, Nil) before you can construct Cons (c, ...) 
> etc.  It's the innermost expression, so evaluating it first makes sense 
> in any sensible evaluation order.


Ignoring efficiency concerns, may I suggest that the correct way to
build lists is by appending elements, not prepending them:

# let append (element,list) = list @ [element];;
val append : 'a * 'a list -> 'a list = <fun>
# append('d', append('c', append('b', append('a', []))));;
- : char list = ['a'; 'b'; 'c'; 'd']

This will evaluate in the right order.

Fernando