How to implement Varient/Tagged Unions/Pattern Matching in Python?

[Aahz]

In article <358b227c-d836-4243-b79a-57258590a7a7 at a10g2000pre.googlegroups.com>,
metal  <metal29a at gmail.com> wrote:
>
>I want to get pattern matching like OCaml in python(ref:http://
>en.wikipedia.org/wiki/Tagged_union)
>
>I consider the syntax:
>
>def decl():
>	def Plus(expr, expr): pass
>	def Minus(expr, expr): pass
>	def Times(expr, expr): pass
>	def Divide(expr, expr): pass
>	def Value(str): pass
>	@enum
>	def expr(Plus, Minus, Times, Divide, Value): pass
>	declare_types(locals())
>
>def f(e):
>	def _Plus(l, r):
>		return '(%s+%s)' % (l, r)
>	def _Minus(l, r):
>		return '(%s-%s)' % (l, r)
>	def _Times(l, r):
>		return '(%s*%s)' % (l, r)
>	def _Divide(l, r):
>		return '(%s/%s)' % (l, r)
>	def _Value(x):
>		return x
>	try:
>		match(e, locals()) # visitor pattern
>	except NoMatchedError:
>		pass

Perhaps you want to define what match() does?
-- 
Aahz (aahz at pythoncraft.com)           <*>         http://www.pythoncraft.com/

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