Ant: [Caml-list] Efficiency of let/and

[Martin Chabr <martin_chabr@yahoo.de>]

As it appears to me, there is no semantic difference
between both alternatives. It can be shown with two
dependent expressions y = 1 and z = y + 2:

# let y = 1 in
  let z = y + 2 in
  z;;
- : int = 3

# let y = 1
  and z = y + 2 in
  z;;
- : int = 3

The order is important in both cases:

# let z = y + 2 in
  let y = x + 1 in
  z;;
Characters 8-9:
  let z = y + 2 in
          ^
Unbound value y

# let z = y + 2
  and y = 1 in
  z;;
Characters 8-9:
  let z = y + 2
          ^
Unbound value y

So the "and"-form depends on the order as well and I
think the syntactic difference can be just used for
documentation. A good idea, by the way.

I hope this helps

Martin



--- Brian Hurt <bhurt@spnz.org> schrieb:

> 
> Say I have two variables I want to set- variable a
> to the value expr1 and 
> variable b to the value expr2.  The two expressions
> are pure (no side 
> effects), and neither one depends upon the other
> (neither expr1 nor expr2 
> contain either a or b as a value), so they can be
> evaluated in either 
> order or in parallel with no harm.  With expressions
> like these, I've 
> gotten into the habit of using let/and to express
> the parallelism, that is 
> I go:
> 
>  	let a = expr1
>  	and b = expr2
>  	in
>  	...
> 
> rather than:
>  	let a = expr1 in
>  	let b = expr2 in
> 
> So my question is: is there any value (other than
> the documentation value) 
> in doing this?
> 
> Just wondering.
> 
> Brian
> 
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