When thinking about trees, I find it's often best to start with the most
basic case. So in your case, begin by writing a function that deals with a
single operator and two numerical arguments:

    (f '(* 4 9)) => (36 4 9)
    (f '(- 6 10)) => (-4 6 10)

Next, consider the case where you have two precomputed lists instead. So
assume you have list arguments that have already been transformed:

    (g '(+ (36 4 9) (-4 6 10))) => (32 (36 4 9) (-4 6 10))

Then think on how to create a function that deals with both instances. So:

    (h '(+ 10 (36 4 9))) => (46 10 (36 4 9))

Once you have a function that can do all that, then think of how you deal
with lists that *haven't* been transformed:

    (i '(+ 10 (* 4 9))) => (46 10 (36 4 9))

And you'll have your answer. Hopefully that's a good enough hint! If you
get stuck on any of those steps, try posting the code you have so far.

- James

On 14 November 2015 at 14:16, <stevegarrid1...@gmail.com> wrote:

> I have recently started learning lisp and completed some simple exercises
> that are available to me, unfortunately I have got stuck & after spending
> hours it seems I don't seem to be getting any closer to a decent solution.
>
> I am trying to produce a function which takes the expression 'tree' as its
> argument and returns the tree with the relevant calculated values in place
> of the operators.
>
> An example of what a tree could look like is: (* (+ 10 (* 4 9)) (- 6 10))
> And the function should return: (-184 (46 10 (36 4 9)) (-4 6 10))
>
>
>
> could anyone help me out with an example to point me in the right
> direction with an explanation of how it works?
>
>
> thanks
>
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