I think Scala has this optional laziness too.
The problem with default-strictness is that libraries that are built with no laziness in mind turn up to be too strict.
Going from lazy to strict is possible in the client side, but the other way is impossible.



2013/8/22 Tom Ellis <tom-lists-haskell-cafe-2013@jaguarpaw.co.uk>
On Thu, Aug 22, 2013 at 12:51:24PM -0300, Thiago Negri wrote:
> How hard would it be to lift strictness annotations to type-level? E.g.
> instead of
> f :: Int -> Int
> f !x = x + 1
> write
> f :: !Int -> Int
> f x = x + 1
> which would have the same effect. At least it would be transparent to the
> developer using a particular function.

See also the recent Reddit thread

    http://www.reddit.com/r/haskell/comments/1ksu0v/reasoning_about_space_leaks_with_space_invariants/cbsac5m

where I and others considered the possibility of a strict language with
explicit thunk datatype.  NB OCaml essentially already has this

    http://caml.inria.fr/pub/docs/manual-ocaml/libref/Lazy.html

but I think Haskellers would do it better because we have a lot of
experience with purity, laziness and monad and comonad transformers.

Tom

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