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Today's Topics:
1. Numeric Integer vs Integer (goforgit .)
2. Re: Numeric Integer vs Integer (Brandon Allbery)
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Message: 1
Date: Mon, 21 Sep 2015 20:23:33 +0200
From: "goforgit ." <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] Numeric Integer vs Integer
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Hello!
Could someone explain to me the difference between the following?
data Atype = Numeric Integer | A | B C
and
data Atype = Integer | A | B C
Thanks in advance!
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Message: 2
Date: Mon, 21 Sep 2015 14:39:51 -0400
From: Brandon Allbery <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Numeric Integer vs Integer
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On Mon, Sep 21, 2015 at 2:23 PM, goforgit . <[email protected]> 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
[email protected] [email protected]
unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net
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