[Haskell-cafe] a simple question about types

[Daniel Fischer]

On Wednesday 17 November 2010 20:19:17, Ryan Ingram wrote:
> Now of course, the followup question is "what the heck is a
> monomorphism restriction and why would I want it?"
>
> Here is a simple example:
<snip>
>
> But if you give g the more general type signature, the
> expensiveComputation has to get run *every time g is called*.  This is
> because there's no way to create a single storage cell for c; there's
> a possible answer for every single type that is an instance of Num.
>
> f makes it clear; c does not get evaluated until the arguments are
> saturated and is locally allocated.  So it's alright to give it the
> polymorphic type.
>
>   -- ryan

That's a most excellent example, thanks.
I hope I find it the next time the topic comes up.