How to declare a Typeless Function

[Fernan Bolando]

Hi

I have a function that swaps rows of an array of double

swap :: Array (Int,Int) Double -> [Int] -> Array (Int,Int) Double

I then create a function that swaps rows of arrays of Complex Double

swap :: Array (Int, Int) (Complex Double) -> [Int] -> Array (Int, Int)
(Complex Double)

In reality the function swap does not care whether its working on a
double or a complex number.
how do I declare swap so that it will work whether it's a complex or a
double array.

I tried googling but I wasn't sure what to google.

fernan
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[Alexander Dunlap]

swap :: Array (Int, Int) a -> [Int] -> Array (Int, Int) a

The lowercase "a" means that that type variable is polymorphic, i.e.
it can be any type.

Alex

On Thu, Jul 2, 2009 at 8:05 PM, Fernan Bolando<fernanbolando@...> wrote:

> Hi
>
> I have a function that swaps rows of an array of double
>
> swap :: Array (Int,Int) Double -> [Int] -> Array (Int,Int) Double
>
> I then create a function that swaps rows of arrays of Complex Double
>
> swap :: Array (Int, Int) (Complex Double) -> [Int] -> Array (Int, Int)
> (Complex Double)
>
> In reality the function swap does not care whether its working on a
> double or a complex number.
> how do I declare swap so that it will work whether it's a complex or a
> double array.
>
> I tried googling but I wasn't sure what to google.
>
> fernan
> --
> http://www.fernski.com
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@...
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>

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[Magnus Therning]

On Fri, Jul 3, 2009 at 4:43 AM, Alexander
Dunlap<alexander.dunlap@...> wrote:
> swap :: Array (Int, Int) a -> [Int] -> Array (Int, Int) a
>
> The lowercase "a" means that that type variable is polymorphic, i.e.
> it can be any type.

Another option would be to simply not put in type of 'swap', load it
in ghci and see what the compiler says the type is :-)

/M

> On Thu, Jul 2, 2009 at 8:05 PM, Fernan Bolando<fernanbolando@...> wrote:
>> Hi
>>
>> I have a function that swaps rows of an array of double
>>
>> swap :: Array (Int,Int) Double -> [Int] -> Array (Int,Int) Double
>>
>> I then create a function that swaps rows of arrays of Complex Double
>>
>> swap :: Array (Int, Int) (Complex Double) -> [Int] -> Array (Int, Int)
>> (Complex Double)
>>
>> In reality the function swap does not care whether its working on a
>> double or a complex number.
>> how do I declare swap so that it will work whether it's a complex or a
>> double array.
>>
>> I tried googling but I wasn't sure what to google.
>>
>> fernan
>> --
>> http://www.fernski.com
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@...
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe@...
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>

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[Joe Fredette]

It's important to note that such a function is not "Typeless" but rather
"Polymorphic" -- that is, it is a type which can be satisfied for many
values of it's type variables.

For instance, the function `(+) :: Num a => a -> a -> a` is polymorphic,
since it's one type variable can be satisfied by any instance of the
`Num` class. It's not that
the `(+)` function is "Typeless" (implying that it has no type)
precisely the opposite, it has _many_ types. Haskell is clever enough to
figure out which one you mean as you use it (most of the time, anyway).

/Joe

Magnus Therning wrote:

> On Fri, Jul 3, 2009 at 4:43 AM, Alexander
> Dunlap<alexander.dunlap@...> wrote:
>  
>> swap :: Array (Int, Int) a -> [Int] -> Array (Int, Int) a
>>
>> The lowercase "a" means that that type variable is polymorphic, i.e.
>> it can be any type.
>>    
>
> Another option would be to simply not put in type of 'swap', load it
> in ghci and see what the compiler says the type is :-)
>
> /M
>
>  
>> On Thu, Jul 2, 2009 at 8:05 PM, Fernan Bolando<fernanbolando@...> wrote:
>>    
>>> Hi
>>>
>>> I have a function that swaps rows of an array of double
>>>
>>> swap :: Array (Int,Int) Double -> [Int] -> Array (Int,Int) Double
>>>
>>> I then create a function that swaps rows of arrays of Complex Double
>>>
>>> swap :: Array (Int, Int) (Complex Double) -> [Int] -> Array (Int, Int)
>>> (Complex Double)
>>>
>>> In reality the function swap does not care whether its working on a
>>> double or a complex number.
>>> how do I declare swap so that it will work whether it's a complex or a
>>> double array.
>>>
>>> I tried googling but I wasn't sure what to google.
>>>
>>> fernan
>>> --
>>> http://www.fernski.com
>>> _______________________________________________
>>> Haskell-Cafe mailing list
>>> Haskell-Cafe@...
>>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>>
>>>      
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe@...
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>>    
>
>
>
>  

[jfredett.vcf]

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