Function fn_bindings 

pub fn fn_bindings(
    fn_id: usize,
    type_args: &[DataType],
    state: &State<'_>,
) -> BindingFrame

The type parameters bound while a function’s body is compiled: what its enclosing impl block fixed, plus what the call site named.

A parameter neither of them mentions is recorded as unnamed, which stands for any. A call never has to name its type arguments, so signal("x") and signal<any>("x") compile the same body; without this the body could not write T in a type position at all.