[m-rev.] for review: improve purity documentation

[Fergus Henderson]

On 06-Mar-2002, Tyson Dowd <trd at cs.mu.OZ.AU> wrote:
>  @item impure
> -Impure predicates may do almost anything, including changing the state of the
> -computation.
> +Impure predicates may perform IO, modify hidden state, and modify the
> +operational semantics of other code.  They may not change the
> +declarative semantics of pure code.

I suggest

	Impure predicates may perform I/O or modify hidden state,
	even if these side effects alter the operational semantics
	of other code.	However, impure predicates may not change
	the declarative semantics of pure code.

> +Programmers should be very careful about mixing code that is promised
> +pure with the impure predicates or functions that may manipulate the
> +same hidden state

s/the impure/impure/

> (for example, the impure predicates used to implement 
> +a predicate that is promised pure); the promise pure is supposed to
> +promise that impure code cannot change the declarative semantics of pure
> +code.

s/the promise pure/the @samp{promise pure} declaration/

Otherwise that looks good, thanks.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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