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

[Don Stewart]

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