> injecting values constructed dynamically

You can also do this with default arguments, e.g. like so:

   let f x y = 
      let g (a = x+1) b = ...
      ...

For example the following is valid OCaml:

   let bump ?(step = 1) x =
     let waa ?( a = step+17 ) b = a * b in
     x + step + waa 666;;

Here the function waa has a default argument whose default argument depends on bump's default argument.

> recursive/derived implicits

Recursion is quite restricted, for example this is not valid Scala:

    def f ( x : Int ) ( implicit y : Int ) : Int = {
      implicit val a = 17
      f ( x+1 ) }

Your example of nested functions with default arguments does not correspond to what derived implicits do. As a result of implicit resolution, an expression with an arbitrary number of subexpressions may be synthesized, the shape of which depends on the types involves. Default parameters simply cannot do that.

The example you give to justify "recursion is quite restricted" is not a restriction on recursion at all, it's an ambiguity problem. Define `a` as `y` to shadow the function parameter, and it compiles.

> does not correspond to what derived implicits do

I did not claim it did. The first example disproved ionforce's claim that default values cannot be constructed dynamically.

> Define `a` as `y` to shadow the function parameter,

Whoops, yes that's correct. I didn't realise this was possible.

> The first example disproved ionforce's claim that default values cannot be constructed dynamically.

But I don't think that is what they meant. I think they meant something along the lines of what I said above:

> an expression with an arbitrary number of subexpressions may be synthesized, the shape of which depends on the types involves

OK, maybe I misunderstood ionforce. I don't deny that type-driven synthesis is a core element of implicits.