RE: [External] : Re: Instead of pcase

[Drew Adams <drew.adams@oracle.com>]

>   > It might be clearer if clauses that can end
>   > the `cond*' are easily distinguished from
>   > those that always continue on to the next
>   > clause - their return value doesn't matter to
>   > the control flow (e.g., they just match/bind).
> 
> That is rather abstract, and I am not sure what idea you are
> proposing.  If you send a specific proposal I can think about it.

I'm not proposing anything there.  I'm saying that
your introduction of fall-through clauses that can't
end the cond* (and thus provide its value) introduces
complexity and can cause confusion.

In terms of a proposal: If you're going to allow
clauses that just "fall through" (e.g. only match &
bind), then (1) tell users how to easily recognize
them and (2) maybe even add something syntactic that
distinguishes them more easily.

>   > Or is the former always the case if a clause
>   > contains two successive sexps?
> 
> I am not sure what "the former" refers to.  Could you please state
> your point in a way that takes less work to understand?

"Former" here refers to clauses that can end the
cond*.  The "latter" kind of clauses cannot; they
always "fall through" (whether or not they perform
some action, such as matching/binding).

What distinguishes a clause that can end the cond*?
How can you tell immediately, independent of what
some sexp is/does, whether the clause it's in can
possibly end the cond* and provide its return value?

That's my question.

I guessed that this possibility is the case whenever
a clause contains only _one sexp_.  If so, that's OK,
but then say that.  And even so, it might be good to
have some clearer indication, to distinguish such
clauses.

Others have already spoken to the oddity of clauses
that can "fall through", that can't, themselves, end
the cond*.  Make it clearer when this is the case -
especially for a construct whose name is so similar
to cond's.  In a traditional `cond' each clause can
potentially end the cond and provide its return value.