Re: [Caml-list] syntactic detail

[oliver <oliver@first.in-berlin.de>]

On Wed, Feb 08, 2012 at 02:12:01PM +0000, David House wrote:
> On Wed 08 Feb 2012 01:58:18 PM GMT, oliver wrote:
> >>Perhaps this could happen. But I feel this could be expressed
> >>equally clearly using some other mechanism, like a comment. We don't
> >>have to have syntax-level support for every weird thing people would
> >>like to do.
> >
> >If something is a weird thing often lies in the eye of the beholder.
> 
> My definition of "weird" is "few people use this in practice".
> 
> Clearly, delimiting groups of thousands is useful to a lot of
> people. But it hides bugs, because if you see 10_000_0000 you are
> much more likely to think it is 10^7 than you are with 100000000,
> where you are likely to be careful and take your time. We can
> prevent this by more stringent syntax rules. This would also prevent
> some corner cases that you have described, that probably barely
> anyone cares about. It's not a free restriction, but it is cheap,
> and definitely has value.

Not sure if it's cheap.
Don't know how much effort it needs to implement it.
But also don't see if it really is that important.


> 
> >An int-value which raises an exception on overflow would be something
> >much more important than making this syntax rule more restricted.
> 
> That's completely orthogonal.
[...]

Orthogonal when looking at the features itself, but not when looking
at the importance of a need of the implementation.


> 
> >It's also somehow weird, to write   1_000_000_000 instead of 1000000000.
> >Why should this weird "_" stuff supported at all?
> >
> >Writing +. instead of + also might be weird from a certain view.
> >So you are using a weird language.
> 
> I think this is addressed by my definition of "weird" above.

No.

of course +. must be used frequently, because it's the notation
that you need for float value addition.

So it's not a rare case; it's what you need to use when
you want to add float values in OCaml.
I doubt that most people only use int values in their code ;-)


> 
> >>>Why should this case be forbidden?
> >>
> >>Because it is impossible to distinguish it from the
> >>wrongly-deliminated case that I described, which leads to the bugs I
> >>described.
> >[...]
> >
> >
> >But that case is just a typo, like it would be without any "_".
> 
> I don't understand. Wouldn't it be better to have a syntax where it
> is harder to make typos?

Yes.

The kind of type you have mentioned here seems to be based
in the allowance of "_" at all, or because you used that "_" feature
without being very used to the consequences of it, when changing code
is necessary.

More to that in a different mail.


> 
> >For some rsearch it might make sense to delimit those digits which
> >are officially rounded in a setting from those which might be rounded.
> >
> >like
> >
> >    4.526829898
> >   vs.
> >    4.5_26829898
> >   vs.
> >    4.52_6829898
> >
> >and so on.
> >
> >So, even you have a floating point value with 9 digits after the
> >decimal point, if you have a case where your official rounding
> >is one or two digits, but you have to use the correct value,
> >you could clarify this in the code.
> 
> This could also be done, by, e.g., defining a new type with explicit
> coercions:
> 
> module Two_dp_float : sig
>  val of_float : float -> t
>  val to_float : t -> float
> end = struct
>  type t = float
>  let of_float x = x
>  let to_float x = x
> end
[...]

I don't see where this addresses my example.


> 
> This actually enforces that you get the notation right in your code,
> rather than with the underscores, where you could typo and put the
> underscore too far right, or forget to put them in all together.

Not sure if you know what I was talking about.
But maybe my example was misleading or not well explained.

> 
> But more generally, I think it is worth more, in terms of bugs
> saved, to restrict the syntax versus allowing these
> infrequently-used cases.
[...]

Not sure if using "_" at all is done frequently.

Maybe a survey should clarify this; otherwise it's just a statement
on frequently used vs. not frequently used, based on your personal assumptions.



Ciao,
   Oliver