[Agda] when with-abstraction fails?

[Jason Hu]

Hi all,

I realize that in some situations, with-abstraction does nothing. E.g.

a-function x y z
  with a-term-that-is-in-the-goal
...  | x = ?

The with-abstraction does not report any error, but rather it does nothing. I know that in some situation with-abstraction is impossible but in those cases, Agda would throw an error. However, in other cases, a tiny bit of change in the code would just turn with-abstraction into a noop and I don’t know why.

I do encounter situations like this in my real project but I do not know how to concentrate a minimal reproducible example. However, I do realize the following methods might or might not solve this problem:


  1.  Add more arguments to the function to a point where everything involved in a-term-that-is-in-the-goal  appears in the argument list.
  2.  If the previous method still doesn’t work (as it happens at this moment), then it seems to have something to do with deeply nested where clauses, e.g. if the example function above is in a where clause, then moving it outside of the where clause will almost certainly make the with-abstraction work again.

As a consequence of this problem, rewrite will also cease to work. Should I consider this a bug (which I really intend to) or is there some behavior that I don’t understand in Agda?

Thanks,
Jason Hu

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