On Monday 26 May 2008 13:22:04 Richard Jones wrote:
> With this definition:
>
>   type 'a t = float
>
> Why is this allowed?
>
>   # ((3.0 : unit t) : string t) ;;
>   - : string t = 3.
>
> Note that unification is prevented if t is opaque, eg, hidden behind a
> module signature.

Because your accessible definition allows you to replace 'a t with float for 
any 'a, which allows you to replace both of your types with float and, 
therefore, they must unify.

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/products/?e