[Haskell-cafe] Mutual scoping question

[Todd Wilson]

It seems (surprisingly to me) that such pattern matches are allowed at the
top level, so that would simplify my kludge a bit by skipping the
definition of fg. But is using pairs (or the equivalent) in this way the
only solution? I was hoping that there might be some kind of top-level
definition syntax like

{f .. = ... ; g .. = ...} where h .. = ...

 that would correctly capture the scoping I'm looking for.

--Todd

On Wed, Nov 22, 2023 at 5:43 PM Jeff Clites <jclites at mac.com> wrote:

> Can you do:
>
>   (f, g) = let f’ = … in (f’, g’)
>
> or is a pattern match not allowed at top level?
>
> Jeff
>
> On Nov 22, 2023, at 4:40 PM, 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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