Two data types are `Coercible` (as in Data.Coerce) if their representation in memory is the same: they are representiationally equivalent You ask for looser structural isomorphism, consider e.g. 

    data B b = B {-# UNPACK #-} !Int b

and

    (Int, b)

The values of these types have quite different representation/memory layout.

- Oleg

On 25 Feb 2019, at 16.38, Georgi Lyubenov <godzbanebane@gmail.com> wrote:

Greetings!

Is there any reason behind/what is the reason behind
```
data A a b = A a b
```
and
```
(a, b)
```

not being coercible?

And in general all n-ary constructors not being coercible to one another?

Thanks in advance!

=======
Georgi

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