On Mon, Apr 23, 2018 at 09:23:58AM +0200, Marc Busqué wrote:
On Sun, 22 Apr 2018, Tom Ellis wrote:
Unless I am much mistaken `Cols s a` is just `a`[1,2]. That explains why the type is ambiguous. There's nothing that fixes `s`.
I also thought that, but if I substitute `Cols s a` by `a`, then the compilation error is:
I had an error in what I said and also it was imprecise. It's `Res (Cols s a)` which is `a`, but only in the cases where you're actually going to use it, and the compiler cannot take that into account when solving the constraint. Anyway, as Li-yao Xia points out in a sibling message, the type variable `s` in not constrained and therefore it seems impossible to solve.
Also, notice that the inferred type does differentiate between `Cols s a` and `a`.
Can you show us a minimal example of `list` working? I'm quite confused about how it could work. [...]
Thanks, but could you send a full working version that includes a definition of `list`? I can't replicate what you've done on my end. Tom