[Zope-dev] Re: [Vote] PEP308 voting began

[Evan Simpson]

Guido van Rossum wrote:
> IMO TALES should solve this for itself by introducing an if/then/else
> expression form rather than depending on Python.  If you can have a
> "not:.." expression, surely you can have an "if:..:then:..:else:.."
> expression.

Now that you point it out, it's not even hard.  Here's a 
proof-of-concept, with really awful parsing (it obviously breaks on 
nested if: then: else:), that actually works:

class IfExpr:
     def __init__(self, name, expr, compiler):
         self._s = expr = expr.lstrip()
         m = re.match('(.*) then:(.*) else:(.*)', expr)
         if m is not None:
             condexpr, thenexpr, elseexpr = m.groups()
         self._cond = compiler.compile(condexpr)
         self._then = compiler.compile(thenexpr)
         self._else = compiler.compile(elseexpr)

     def __call__(self, econtext):
         if econtext.evaluateBoolean(self._cond):
             return econtext.evaluate(self._then)
         return econtext.evaluate(self._else)

(Tested with
<div tal:replace="if:options/x then:string:yes else:string:no">)

Is this worth a robust implementation, ZPT folks?

Cheers,

Evan @ 4-am