I don't see how this extrapolates to arbitrary, extended match
expressions? You're proposing a slightly more flexible switch, which match
is only intended to be as the most basic case. Even if you purely swapped
it out with any the various proposals for identifying a constant vs a
target, it's still far more verbose than any of them.
On Sat, Jul 4, 2020 at 4:31 PM Shantanu Jain <hauntsani...@gmail.com> wrote:
> Thank you for this PEP! Pattern matching is really exciting.
>
> As the PEP mentions and the thread evidences, the current dot syntax for
> the “constant value pattern” is a tricky point. Given this, I thought I’d
> throw another suggestion into the bikeshed.
>
> Use percent placeholder to indicate lookup (or even eval) semantics for a
> given name. For example:
> ```
> FOO = 1
> value = 0
>
> match value:
> case %(FOO): # This would not be matched
> ...
> case BAR: # This would be matched
> ...
> ```
> I like this syntax because it’s reminiscent of named substitution in
> percent formatted strings. It suggests a substitution / placeholder
> metaphor that is quite fitting. It has the benefit of not introducing a new
> symbol into Python and being explicit and hard to miss, including in nested
> contexts.
>
> Note, it seems like it would also be technically possible to use curly
> braces (the more idiomatic means of named substitution in Python 3):
> ```
> case {FOO}: …
> ```
> The main downside of this is that it could look like some sort of
> singleton “set pattern” (note that the PEP only supports “sequence
> patterns” and “mapping patterns”).
> (But set patterns maybe don’t quite make sense + if your set pattern had
> multiple elements you’d still get a SyntaxError. For other examples where
> something in Python looks like a set literal but isn’t, refer to `{}` and
> f-strings, so it’s maybe not the biggest stretch)
>
> Both of these suggestions could also allow us more flexibility for
> constant value patterns, since currently there isn't a good way to match
> against a constant expression. For example, we could extend this syntax to
> allow us to express:
> ```
> case %(2 ** 10): ...
> ```
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