Re: [Haskell-cafe] a simple question about types

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.