[Haskell-cafe] a really juvenile question .. hehehehe ;^)

[Galchin, Vasili]

ok ... by using "newtype", we are constricting/constraining to a subset of
CInt .. e.g. something like a "subtype" of CInt?? (where by "subtype", I
mean like the notion of subtype in languages like Ada). For our audience,
can you perhaps distinguish (in a typeful way) between the Haskell notion of
"type", "newtype" and "data"? Or maybe let's distinguish between these
notions not only in a typeful manner, but also in a historical motivation?
.. ...  motivations are always IMO very, very enlightening!


Regards, vasili

On Mon, Oct 6, 2008 at 12:47 AM, Don Stewart <dons at galois.com> wrote:

> Used wisely, newtype prevents accidentally constructing illegal values
> of Signal type, by treating them as CInts. You can restrict the valid
> values of the Signal type to be just those signals you define, not
> arbitrary bit patterns that fit in a CInt.
>
> vigalchin:
> >    Thanks Don. Maybe both for me and others in order to take the fight to
> the
> >    Klingons and other Baddies, please explain the "typefulness"
> protection
> >    that "newtype" affords over the "Klingon " "type" ...  In the code
> that I
> >    contributed to the library, I like to think that I used "newtype"
> >    appropriately but not perhaps with full understanding.
> >
> >    Thanks, Vasili
> >
> >    On Mon, Oct 6, 2008 at 12:37 AM, Don Stewart <[1]dons at galois.com>
> wrote:
> >
> >      vigalchin:
> >      >    Hello,
> >      >
> >      >       I am reading some extant Haskell code that uses Posix
> >      signals.... I am
> >      >    confused by the motivation of the following ...
> >      >
> >      >    type [1]Signal = [2]CInt
> >      >    [3]nullSignal :: [4]Signal
> >      >    [5]internalAbort :: [6]Signal
> >      >    [7]sigABRT :: [8]CInt
> >      >    [9]realTimeAlarm :: [10]Signal
> >      >    [11]sigALRM :: [12]CInt
> >      >    [13]busError :: [14]Signal
> >      >    [15]sigBUS :: [16]CInt
> >      >
> >      >    OK .. "type" is really just a synomym and doesn't invoke type
> >      checking
> >      >    like "data" type declarations do .. so why don't we have all
> the
> >      "CInts"
> >      >    substituted by "Signal"? I.e. what did I miss?
> >
> >      Looks like it should all be Signal, and probably should be using a
> >      newtype, to prevent funky tricks. The Posix layer is a bit crufty.
> >      -- Don
> >
> > References
> >
> >    Visible links
> >    1. mailto:dons at galois.com
>
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