Re: P1788 1.8 "Language considerations"
Nick, Vincent, P1788
On 5 Dec 2012, at 09:28, Vincent Lefevre wrote:
> I have two comments concerning §1.8:
>
> 1. Its first paragraph is:
>
> All relevant languages are based on the concepts of data and
> transformations. In Von Neumann languages, data are held in
> variables, which are transformed by assignment. In functional
> languages, input data are supplied as arguments; the transformed
> form is returned as results. Dataflow languages vary considerably,
> but use some form of the data and transformation approach.
>
> Actually this is not quite true or not well formulated, IMHO. In
> Von Neumann languages, one also has control. In functional languages,
> one can also return functions, which are not just a transformation
> of the inputs, but also depend on the context (notion of closure).
> I think that what really matters is that all languages can incorporate
> the dataflow model, even though they can do more. The first sentence
> could be changed to something like:
>
> All relevant languages use, among others, the concepts of data and
> transformations.
That change looks good to me.
> 2. The second paragraph seems to be about the approximation of real
> arithmetic. But in P1788, intervals can be used for other things,
> such as range computation.
That seems a fair point. In view of range computation's importance in global optimisation, Nate Hayes' branch & bound algorithms, etc., it should not be excluded; the current wording does rather exclude it.
And I had a related reservation about the sentence after item (4): "Specifically, if the data before and after ... posterior set." This is a description of the behaviour of interval *arithmetic operations* -- interval extensions of real point functions.
I would welcome a rephrasing to recognise that the standard specifies other interval operations, such as intersection & convexHull, as well as ones that transform interval(s) to a non-interval: midpoint, comparison operations, etc.
I don't think we need much, if any, new material; rather a rewording that manages to be more inclusive.
John Pryce