[Haskell-cafe] Mutual scoping question

[Todd Wilson]

Thanks, Mark. I wanted f and g to be defined at the top level for use
throughout my whole file, rather just inside of a let. Of course, I could
also put the definitions of f, g, and h in their own module/file that hides
the name h and then import this, but I was hoping to have this all in
one place.

--Todd

On Wed, Nov 22, 2023 at 5:26 PM Mark McConnell <mmcconnell17704 at yahoo.com>
wrote:

> What about
>
> let h ... = ... h ...
> in let f ... = ... f,g,h ...
>        g ... = ... f,g,h ...
>    in ... (main body that uses f and g) ...
>
> This makes the dependencies clear.  h stands on its own, f and g use each
> other together with h, and the main body can use f, g, and h.
>
> I believe what you wanted, however, was to express that the main body
> *cannot* (will not, should not) use h.  This version does not express that.
> On Wednesday, November 22, 2023 at 07:40:25 PM EST, Todd Wilson <
> twilson at csufresno.edu> wrote:
>
>
> Hello, Cafe:
>
> Is there a preferred way to define two top-level mutually recursive
> functions, f and g, that both use a common local function h such that h is
> (1) only defined once and (2) does not escape the scope of f and g? I
> suppose it could be done like this:
>
> fg = let f ... = ... f,g,h ...
>          g ... = ... f,g,h ...
>          h ... = ... h ...
>       in (f,g)
> f = fst fg
> g = snd fg
>
>
> but is there something more elegant than this that I'm not seeing?
>
> Todd Wilson
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