Re: EXTERNAL: Re: [vhdl-200x] Update to proposal for arbitrary integers

2014-10-29 9:34 GMT+01:00 Martin.J Thompson <Martin.J.Thompson@trw.com>:
>
> Python (sorry to use it as an example again!) has the concept of “None”
which is a metavalue used for this sort of purpose.
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>
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> We could use None, Nothing, Invalid_Value, Undefined or some other
similar phrase (obviously, there’s the risk of collision with historically
code).
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> The phrase “Undefined” would have some correspondence with ‘U’ in
std_logic. Hmm.  Would we then make these numerical type initialise to
“Undefined” rather than type’low??


If you open up the language to Nullable types you open up a giant can of
worms and errors. If this sort of functionality in VHDL is need I suggest
that it is based on the option type known from functional programming
languages such as Haskell. Only then will you be able to rely on the
compiler avoid null-exceptions. Of cause a Maybe (Haskell) or Option (F#)
type would require significant modifications to the VHDL type system, but
it opens up a whole new world of possibilities.

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