[haskell-cafe] Monad and kinds

Jules Bean jules at jellybean.co.uk
Fri Sep 5 04:34:35 EDT 2008

Jake Mcarthur wrote:
> On Sep 4, 2008, at 9:52 PM, Tim Chevalier wrote:
>> I'm no master, but I've never encountered a situation where strictness
>> annotations would be useful as documentation, nor can I imagine one.
> I'm no master either, but how about these simple examples?
>         data Stream a = Cons !a (Stream a)
>         data Vector3 a = Vector3 !a !a !a
> The compiler will certainly be able to infer the strictness itself in
> most uses, so obviously the purpose for these annotations is not for
> optimization, but I still would find these annotations useful.

As far as I am aware this statement is false.

I do not believe the compiler infers strictness in common uses of either 
of these cases, and I have seen space blowups / stack blowups because of it.

I use the rule of thumb : simple 'scalar' field components should be strict.

Scalar is an ill-defined term but typically means non-recursive data 
types, like Int and Bool.

The most natural exception to this rule is the 'memoizing constructor' 


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