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@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@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
_______________________________________________
Haskell-Cafe mailing list
To (un)subscribe, modify options or view archives go to:
http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
Only members subscribed via the mailman list are allowed to post.