Monomorphism, monomorphism...

[Marcin 'Qrczak' Kowalczyk]

09 Oct 2001 13:55:04 -0700, Carl R. Witty <cwitty@newtonlabs.com> pisze:

> The TREX paper from Mark Jones and Benedict Gaster (I hope I
> have the names right) had both extensible records and extensible
> variants (extensible variants being what you would need to implement
> downcasts),

I don't think so. Here is how the requirement can be formulated:

We need some type T such that it's possible to define a family of
functions for arbitrary choices of A:
    upA   :: A -> T
    downA :: T -> Maybe A
satisfying downA (upA a) = Just a. We want to choose the type for T
before deciding the exact set of types for A.

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