[m-rev.] For review: State Variable Transformation

[Ralph Becket]

Fergus Henderson, Tuesday,  7 May 2002:
> 
> Saying that something is deprecated is the standardese way of implying
> that it may be removed in a future version, and I don't want DCGs to be
> removed, which is why I object to that wording.
> 
> If you want to make some parenthetical suggestions about programming style,
> I don't object to that, so long as they are clearly labelled as such.

I think it's important to say something along these lines.

> For example, maybe something along these lines:
> 
> 	(Note that if there is only one entity being threaded
> 	through a computation, either DCG notation or state variable
> 	notation could be used.  As a matter of style, we recommend that
> 	state variable notation be used if the entity represents some kind
> 	of state, and DCG notation only be used for actual grammars.)
> 
> However, I'm not entirely happy with these words -- I don't think the
> distinction here is very clear.

How about:

	(DCG notation is intended for writing a particular style of
	parser; in the past it has also been used in non-parsing code to
	thread an implicit state variable, typically the IO state,
	through code.  As a matter of style, we recommend that in future
	DCG notation be reserved for parsing and that state variable
	syntax be used for passing state threads.)

- Ralph
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