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Gleb Alexeyev wrote:
| Mauricio wrote:
|
| data SomeNum = SN (forall a. a)
|
| [...]
|
| you cannot do anything to the value you extract
Maybe. Say you construct (SN x). If you later extract x, you can observe
that it terminates (using seq,
On Wed, 2009-01-21 at 13:38 -0600, Jake McArthur wrote:
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Gleb Alexeyev wrote:
| Mauricio wrote:
|
| data SomeNum = SN (forall a. a)
|
| [...]
|
| you cannot do anything to the value you extract
Maybe. Say you construct (SN x). If you
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Jonathan Cast wrote:
| I think you meant to quote the definition
|
| data SomeNum = forall a. SN a
Quite so. Thanks for clearing that up.
- - Jake
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4294967296 :: Integer
(...)
In the above you can see the polymorphism of the return type of
fromInteger, it returns a Int8 or a Int32.
You can see the polymorphism of the argument of show, it takes an Int8
or Int32 or Integer.
The latest ghc-6.10.1 also allows avoiding use of SomeNum, see
Mauricio wrote:
But how is this:
data SomeNum = forall a. SN a
different from:
data SomeNum = SN (forall a. a)
In the first case the constructor SN can be applied to the monomorphic
value of any type, it effectively hides the type of the argument. For
example, you can have a list like
I just thought that the shorter explanation could do better: the
difference is in the types of the constructor functions.
Code:
{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE RankNTypes #-}
data SomeNum1 = forall a. SN1 a
data SomeNum2 = SN2 (forall a. a)
ghci session:
*Main :t
Great, thanks! I'm enlightened :)
And no one had to hit you with a stick first!
But how is this:
data SomeNum = forall a. SN a
different from:
data SomeNum = SN (forall a. a)
?
At a glance they look the same to me — but only the first is accepted by ghc.
There is also the GADT syntax:
But how is this:
data SomeNum = forall a. SN a
different from:
data SomeNum = SN (forall a. a)
At a glance they look the same to me — but only the first is accepted by
ghc.
Following the link you pointed in the last
message, I found this at 8.8.4.1:
data T a = T1 (forall b. b - b - b) a
If
On Tue, Jan 20, 2009 at 2:51 PM, Mauricio briqueabra...@yahoo.com wrote:
But how is this:
data SomeNum = forall a. SN a
different from:
data SomeNum = SN (forall a. a)
At a glance they look the same to me — but only the first is accepted by
ghc.
Following the link you pointed in the last
On Tue, Jan 20, 2009 at 1:14 PM, David Menendez d...@zednenem.com wrote:
On Tue, Jan 20, 2009 at 2:51 PM, Mauricio briqueabra...@yahoo.com wrote:
But how is this:
data SomeNum = forall a. SN a
different from:
data SomeNum = SN (forall a. a)
At a glance they look the same to me — but
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