[Haskell-beginners] Numeric Integer vs Integer

[goforgit .]

Thanks Brandon, that cleared things up!

On Mon, Sep 21, 2015 at 8:39 PM, Brandon Allbery <allbery.b at gmail.com>
wrote:

>
> On Mon, Sep 21, 2015 at 2:23 PM, goforgit . <teztingit at gmail.com> wrote:
>
>> Could someone explain to me the difference between the following?
>>
>> data Atype = Numeric Integer | A | B C
>>
>> and
>>
>> data Atype = Integer | A | B C
>>
>
> The second one is an enumeration with three values: "Integer" (which is
> *not* an integer, nor does it contain one), "A", and "B" which as written
> there takes a value of some unspecified type C as a parameter.
> The first one is a enumeration with three values: "Numeric" which takes an
> Integer as a parameter, "A", and "B" which takes a value of some
> unspecified type C as a parameter.
>
> Note that the "Integer" in the second one has *nothing whatsoever* to do
> with the *type* Integer.
>
> Remember that you must always provide a data constructor with "data"; you
> cannot simply say "data MyInt = Integer" to "wrap" an Integer, because you
> have not said what to wrap it *in*. (You may have intended to create a type
> alias, though; that would be "type", not "data".) A "data" always requires
> a data constructor name, so the compiler can tell when you are talking
> about a value of that type by looking for the constructor.
>
> --
> brandon s allbery kf8nh                               sine nomine
> associates
> allbery.b at gmail.com
> ballbery at sinenomine.net
> unix, openafs, kerberos, infrastructure, xmonad
> http://sinenomine.net
>
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