I've just discovered what the `@<template_name>` notation in functions like `fetchByKey` et al means

[Luciano]

Here’s an actual example of what I’m talking about above:

Specifying symbol type for `HasField x r a`

Hi Luciano, that’s a very interesting problem. The solution mostly involves sprinkling a few more types across your code. Despite that, you will still need to enable the AllowAmbiguousTypes language extension because the type parameter f only appears within the type class constraints. First of all, you need to tell the compiler that you want to access the x field in updateInner's setField and getField: updateInner : forall x f. (Functor f, HasField x Outer (f Inner)) => (Inner -> Inner) -> Ou…