With default arguments, in the worst case you can do this:
proc f[T](x: typeOrSeqType(proc(y: string): T)) =
discard
proc f() = f(p)
Run
The issue here is generic inference with double generic parameters. In reality,
due to [implicit
generics](https://nim-lang.org/docs/manual.html#generics-implicit-generics),
`f` becomes:
proc f[T; U: typeOrSeqType(proc(y: string): T)](x: U = p) =
discard
Run
Normally `U` can be inferred from the default argument, but there is no
mechanism to infer `T` from `U`. For example, the following works:
proc foo(a: int | string = 3) = discard
foo()
Run
But not this:
proc foo[T; U: T](a: U = 3) = discard
foo()
Run
Unfortunately I can't think of a good workaround other than the manual overload.
