Hi Brett,
Without having really looked at the history of all the languages we
mention in the PEPs, I have a hunch that most of them had pattern
matching from quite the beginning or an early stage on, indeed. That
being said, I think the question itself does not really make much
sense, though. Programming languages are rarely if ever just invented
out of the blue these days, but evolve from other languages that have
gone before them. So, sure C++ and Objective-C both had objects and
classes from the very beginning on, but if we take into consideration
that they strongly build on C, we could argue just as well that OOP
was a later addition to C. It really depends on your point of view.
But since we are talking about different languages here, there is one
example I could bring up. In C#, the underscore is a perfectly legal
variable name. And yet, it is also used as a 'discard' [1] in newer
versions. Moreover, F#, which certainly uses the underscore as a
wildcard, runs on the same platform as C# and thus has to deal with
this, too. Somehow, Microsoft and its developers seem able to cope
with it.
If I may widen the topic here a bit and seize the opportunity to go
beyond just answering your email: I must admit that I find this entire
discussion about the wildcard pattern rather mind-boggling. We seem
all to accept the reality that ``match`` and ``case`` are
context-sensitive keywords (i.e. they are both keywords and legal
names) and that you cannot write ``123.bit_length()`` because the dot
has several different meanings. But when it comes to the underscore
and the idea that *as a pattern* it might simply not store a value, it
is considered an insurmountable obstacle to learning and understanding
pattern matching? Particularly because, after all, the underscore is
in Python only a wildcard *by convention*?
I think pattern matching has a lot in common with 'recursion': if you
see it for the first time, it can be very hard to wrap you head around
it and understand what is going on or why anyone would want to do such
a thing. But once you understood it, it can be an extremely elegant
solution to many problems. So, I really can fully understand a lot of
the reservations brought forward about this feature and various
aspects of it. And there were enough good and valid points brought up
by the community, which we then integrated into and respected in our
overhauled design---but that the wildcard pattern causes so much grief
really is entirely beyond me...
So, yes, most languages had pattern matching quite from the outset on
(or not at all). But then, again, Python is about the only language I
know to have introduced 'type' annotations so late in life rather than
from its very beginning. It came at the cost of using the colon for
something different than compound statements or dictionaries. If we
consider how much annotations have been expanded in more recent
versions of Python and how many tools make good use of it, I would
call that a pretty successful move, though---even though all other
languages might have had type annotations from their very birth.
Kind regards,
Tobias
P.S. Sorry, I guess this turned out to be not so much a reply to your
comment alone, as much more a reply to many a message and discussion
that has been posted here over time.
[1] https://docs.microsoft.com/en-us/dotnet/csharp/discards
Quoting Brett Cannon <br...@python.org>:
On Mon, Nov 16, 2020 at 9:03 AM Tobias Kohn
<ko...@tobiaskohn.ch> wrote:
_Hi Mark,
Thank you for your interest and the questions.
1. This really comes down to how you look at it, or how you define
pattern matching. The issue here is that the concept of pattern
matching has grown into a large and somewhat diverse flock of
interpretations and implementations (as a side note: interestingly
enough, some of the only universally agreed-upon standards are to
use `_` as a wildcard and not to mark names that capture/bind
values---which are quite exactly the points most fiercely debatted
here)._
_How many of those languages added pattern matching /later/ and
not at the earliest stages of the language (if not from the
beginning)? And for those that added it later, how many of those
didn't already have a convention surrounding "_"? My suspicion is
"not many" and "not many". 😉_
_ _
_-Brett_
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