Re: [Caml-list] syntactic detail

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

On Wed, Feb 08, 2012 at 01:09:48PM +0000, David House wrote:
> On 02/08/2012 12:54 PM, Gabriel Scherer wrote:
> >There is no purpose, it's just an edge case of the simple lexical
> >specification you can find at:
> >http://caml.inria.fr/pub/docs/manual-ocaml/lex.html#float-literal
> >
> >Everywhere digits are allowed, you can insert extraneous underscores.
> >There is no restriction that there must be at least one digit for
> >underscores to be valid. I don't see why there should be.
> 
> I would actually prefer a slightly more constrained format. It is
> very easy to typo large numbers like:
> 
>   let ten_million = 10_000_0000 in
> 
> When eyeballing this, it is extremely easy to mistake this as 10^7,
> when it actual fact it is 10^8.
[...]

I think the problem of being confounding 10_000_0000 with 100_000_000
or 10_000_0000 with 10_000_000 is less prominent then confounding
100000000 with 10000000.

So this syntax rule already makes things much easier to read.
That's it's advantage.

To have here all three characters as syntax rule could make sense,
but is less a problem than having no allowance of "_" in numbers at all.


For rare cases it might also make sense to have "_" inserted arbitrarily,
for example in math education or when clarifiying things to others,
it might also make sense to put "_" around the differing values.
So it migth make sense for clarifiying differences and for educational
purposes.

For example you might have a startvalue of an algorithm and the staring value
for a certin behaviour is
  3.36639926549992
but your colleague uses
  3.36639296549992

For clarification one could write:
  3.36639926549992 vs.
  3.36639296549992

or better

  3.36639_92_6549992 vs.
  3.36639_29_6549992

A case, where two digits were switched.


Might not be the case that pops up all to often,
but if so, it might be fine, if both values can be used:

  let startval_correct = 3.36639_92_6549992 
  let startval_wrong   = 3.36639_29_6549992


So I have invented reasons why it's fine as it is.
Why should this case be forbidden?


> 
> I would prefer a syntax rule that only allows underscore every three
> characters (starting at the RHS of the number, i.e. complying to the
> usual convention). Well, certainly that for decimal literals. For
> hex literals you probably want to enforce the same, but every four
> characters.
[...]

For Hex it might also make sense to have it all two characters.

If the rule would be only all 4 characters, that would be bad.

Ciao,
   Oliver