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:.."

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?


Evan @ 4-am

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