Enhanced type guard syntax]

[Peter-Henry Mander]

Thomas Arts wrote:
> Dear Peter

Hi Thomas,

> If you want to extend that principle with user defined types, you
> might do that by tuples and a lot of work, or add something to
> the internal representation. No matter how, you need a representation
> for it.
> 
> Static type checking may use the same representation as the
> dynamic one, but checks at compile time whether there is a 
> type conflict. At runtime there need not be any type information
> available, since you are guaranteed (by the checker) that you
> will never add an integer to an atom.

Thanks for explaining that, I forgot the static/dynamic aspect.

So (including aspects in an email to Vlad) this has an impact on:-

1) code correctness and checking during compilation, without added 
"binary-baggage" at runtime,

2) trapping exceptions at runtime, which is what tagging was meant to 
achieve, albeit clumsily, I concede.

3) optimisation (maybe?).