Re: [boost] Interest in updated expression template library?

Subject: Re: [boost] Interest in updated expression template library?
From: Zach Laine (whatwasthataddress_at_[hidden])
Date: 2017-01-11 14:11:37

On Wed, Jan 11, 2017 at 12:03 PM, Brook Milligan <brook_at_[hidden]> wrote:

>
> > On Jan 11, 2017, at 7:42 AM, Zach Laine <whatwasthataddress_at_[hidden]>
> wrote:
> >
> > On Tue, Jan 10, 2017 at 8:50 PM, Brook Milligan <brook_at_[hidden]> wrote:
> >
> >> It seems that Yap defines the meaning in terms of a set of function
> >> overloads.
> >
> > Yes and no.  There are *implicit* transformations and evaluations that
> work
> > based on extension points/function overloads; there can indeed only be
> one
> > overload that gets selected, and this is implicitly chosen based on the
> > normal overload resolution rules.  There is also the explicit transform()
> > function.  This is what most of the examples use, and it is my preferred
> > and recommended way of doing things.  It allows you to define whatever
> > transforms you like, including transforms that evaluate your expression
> in
> > whole or in part.  You can have as many of these as you like, and there
> is
> > often no need to define a context per se.  I say "per se" because the
> > transform itself often looks much like a Proto context (e.g. it might be
> > stateful).  See the examples in the docs for details.
>
> OK, I get it now.  Your transforms are acting in much the same way that
> Proto contexts act.  They define the interpretation of the expression tree
> when explicitly passed to the evaluate() function.  Perhaps noting the
> connection (in a “comparison with / moving from Proto” section?) is worth
> noting, as I missed it at first.
>
> It seems that the reference documentation for evaluate() does not note
> that the transform argument is optional.  Given your examples that call
> evaluate() with only a single argument, it seems to be optional.  Is that
> also true for evaluate_as()?  Should this be made explicit in the reference
> docs?
>
> Thanks for the clarification.

evaluate() and evaluate_as() do not take a transform.  They only evaluate.
The optional params are used to supply values for placeholders.
 transform() takes a transform though.

Though these points are covered if you read through the examples, it seems
clear to me now that there needs to be a "Transforming and Evaluating
Expressions" section in the tutorial.

Zach