Hi,
I'm new to the list and apologies for going off-topic a bit (this has
nothing to do with performance):
If Python implements switch statements it would be a shame not to have
pattern-matching in switch statements too. This is a feature that has
long been used in functional languages like ML. For example, here's
pattern matching on a tuple:
def foo(a,b):
switch (f(a), g(b)):
case (c,1): something(c) # if g(b)==1, assigns c = f(a)
case (1,d): something(d) # if f(a)==1, assigns d = g(b)
case (c,_): something(c) # any tuple: assigns c = f(a), _ is wildcard
Some syntactic sugar related to this would be a way to pattern-match on
arbitrary objects as is now done with tuples:
def foo(pair, number):
Pair(x,y) = pair # assert isinstance(pair,Pair), assigns x and y
int(i) = number # assert type(x)==IntType, assign i
(To implement this, classes would have a __tuple__ method that returns the
tuple for matching. By convention it should return the arguments to its
__init__ method.)
Note how type-checking happens in a very natural way:
a = int(a) # convert a
int(a) = a # type-check a
Combining the two:
def sum(pairOrInt):
switch pairOrInt:
case int(a): return a
case Pair(x,y): return sum(x)+sum(y)
Here's some documentation on how it's done in Cyclone, a C variant from
AT&T that seems to have a strong ML influence:
http://www.research.att.com/projects/cyclone/online-manual/main-screen005.html
----------------------------------------------------------------------
Brian Slesinsky
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