On 6/23/2020 5:56 PM, Barry Warsaw wrote:
match:
expression
case arm1:
pass
case arm2:
pass
else:
pass
nicely mirrors try/except and if/elif/else constructs so it looks quite natural.
Agreed as to the look of the form.
Some observations:
1. 'else' is equivalent of 'elif True', so two alternative keywords are
not strictly needed. The proposal uses 'case _' as the parallel
catchall to 'elif True'. If '_' were not otherwise being used as a
wildcard, I might suggest that 'case' by itself be used to always match.
2. 'expression' is *not* a general statement, let alone a suite of such,
and it is not natural in non-interactive code that the object resulting
from an expression be magically captured to be *implicitly* referenced
in later code (the patterns).
Even though match may be thought of as a type of multiple elifs, this
has no parallel in if/elif/else statements. However, in try/except
statements, raised exceptions *are* magically captured, to be
*explicitly* referenced in 'except' tuples. 'Try' and 'match' both
consist of a setup, multiple test:action pairs, and a default action.
So a similar indent structure can easily seem appropriate.
3. A bonus of 'match' by itself is that re-based syntax colorizers, as
in IDLE, could pretend that the keyword is 'match:' and avoid colorizing
re.match, etc. Or a colorizer could check that 'match' is followed by
':'. Always colorizing 'case' seems like less of an issue as I think it
is less common as a name.
--
Terry Jan Reedy
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