I am puzzled how functions are handled by type inference. There doesn’t seem to be a type `Function{InputType, ReturnType}`

to help type inference, instead there is a `typeof(f)`

Type. Why is that? I am happy if you point me where to read up on this.

```
julia> h(f::Function, x) = f(x)
h (generic function with 1 method)
julia> code_warntype(h, (Function, Int))
Body::Any
1 1 ─ %1 = (f)(x)::Any │
└── return %1 │
julia> @code_warntype h(abs, 3)
Body::Int64
1 1 ─ %1 = (Base.flipsign_int)(x, x)::Int64 │╻╷ abs
└── return %1 │
julia> @macroexpand @code_warntype h(abs, 3)
:((InteractiveUtils.code_warntype)(h, (Base.typesof)(abs, 3)))
julia> typeof(abs)
typeof(abs)
julia> code_warntype(h, (typeof(abs), Int))
Body::Int64
1 1 ─ %1 = (Base.flipsign_int)(x, x)::Int64 │╻╷ abs
└── return %1
```