[Haskell-cafe] noob question

Ben thefunkslists at gmail.com
Mon Feb 25 19:32:32 EST 2008

On Feb 25, 2008, at 4:11 PM, Philippa Cowderoy wrote:

> On Mon, 25 Feb 2008, Ben wrote:
>> <interactive>:1:8:
>>   Ambiguous type variable `t' in the constraints:
>>     `Fractional t' arising from a use of `/' at <interactive>:1:8-10
>>     `Integral t' arising from a use of `^' at <interactive>:1:7-15
>>   Probable fix: add a type signature that fixes these type  
>> variable(s)
> / doesn't do integer division, so from there it concludes that you're
> working with a Fractional type - Haskell never coerces behind your  
> back,
> so not only the result of / but also its parameters are Fractional.
> ^ only works for Integral types. You might consider that a little
> arbitrary, but hey - it's mostly like that because it's much easier to
> raise something to an integer power.
> There's no default it can pick that's both Fractional and Integral,  
> so it
> doesn't know what type the expression should have and it's asking  
> you to
> tell it ("add a type signature that fixes these type variable(s)"). In
> practice you won't be able to unless you've got a broken number type
> handy, but that's the way things go.

Ok, that makes sense.  There's no num k that's both Fractional and  
Integral, where as in the case where I had the number literals, those  
were two different instances. What's the usual way of working around  
this?  Something like

(\k -> (1/ fromInteger k) ^ k) 3

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