Re: Instead of pcase

[Ihor Radchenko]

Richard Stallman <rms@gnu.org> writes:

>   > Consider another example:
>
>   > (match* (xor (not var) t) t)
>
> Anyway, I suppose the best response is to say that such counterintuitive
> constrained variables are best avoided.  Or else specifically disallow
> `xor' as PRED in a constrained variable.

My point is not about `xor' in particular.
What I am trying to demonstrate is that

(foo (bar var) arg) looks like a normal Elisp call - `foo' called with
two arguments: (bar var) and arg.

Yet, it has completely different meaning inside match*.

So, it is very easy to confuse match* clause result with return value of
the equivalent normal Elisp expression.

In contrast, a more explicit

(match* (constrain var (and (bar var) (foo var arg))) ...) 
(match* (constrain var (and (not var) (xor var t)) t) ...)

is much more natural and avoids confusion.

> ...
> I wonder why people defined `xor'.  It can't be used
> as a conditional, like `and' and `or', so what is the point of it?

`xor' can be used as conditional, and it also comes handy at time (we
have 7 functions using `xor' in Org mode, for example).
But that's off-topic to `pcase' discussion.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
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