Michael Chermside wrote:
> Now the pattern matching is more interesting, but again, I'd need to
> see a proposed syntax for Python before I could begin to consider it.
> If I understand it properly, pattern matching in Haskell relies
> primarily on Haskell's excellent typing system, which is absent in
> Python.
There's no real need for special syntax in Python - an appropriate tuple
subclass will do the trick quite nicely:
class pattern(tuple):
ignore = object()
def __new__(cls, *args):
return tuple.__new__(cls, args)
def __hash__(self):
raise NotImplementedError
def __eq__(self, other):
if len(self) != len(other):
return False
for item, other_item in zip(self, other):
if item is pattern.ignore:
continue
if item != other_item:
return False
return True
Py> x = (1, 2, 3)
Py> print x == pattern(1, 2, 3)
True
Py> print x == pattern(1, pattern.ignore, pattern.ignore)
True
Py> print x == pattern(1, pattern.ignore, 3)
True
Py> print x == pattern(2, pattern.ignore, pattern.ignore)
False
Py> print x == pattern(1)
False
It's not usable in a dict-based switch statement, obviously, but it's perfectly
compatible with the current if/elif idiom.
Cheers,
Nick.
--
Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia
---------------------------------------------------------------
http://boredomandlaziness.skystorm.net
RetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4