[Python-ideas] Infix application of binary functions

[Carl M. Johnson]

Last time, I swear! I caught a bug in the last version. Since I
mutated my instances (not very Haskell-like!!), you couldn’t use the
same function more than once. Here’s a new version that lets you use
the same function again:

class InfixArity(object):
    def __init__(self, arity):
        self.arity = arity

    def __call__(self, func):
        self.func = func
        return self

    def __add__(self, arg):
        return InfixHelper(self.func, self.arity, arg)

    __radd__ = __add__
    __floordiv__ = __rfloordiv__ = __add__
    __truediv__ = __rtruediv__ = __add__

class InfixHelper(object):
    def __init__(self, func, arity, firstarg):
        self.func = func
        self.arity = arity
        self.args = [firstarg]

    def __add__(self, arg):
        self.args.append(arg)
        if len(self.args) < self.arity:
            return self
        else:
            return self.func(*self.args)

    __radd__ = __add__
    __floordiv__ = __rfloordiv__ = __add__
    __truediv__ = __rtruediv__ = __add__


Infix = lambda func: InfixArity(2)(func)

I imagine it would be possible to make an n-arity class that could
work like “average // 1 // 2 // 3 // 4 // done” or maybe one that has
you use a different operator for the last argument, but I leave that
as an exercise for the reader.

-- Carl Johnson

On Wed, Jul 21, 2010 at 5:49 PM, Carl M. Johnson
<cmjohnson.mailinglist at gmail.com> wrote:
> Thought about it some more. Here’s a more general formula:
>
> class InfixArity(object):
>    def __init__(self, arity):
>        self.arity = arity
>        self.args = []
>
>
>    def __call__(self, func):
>        self.func = func
>        return self
>
>    def __add__(self, arg):
>        self.args.append(arg)
>        if len(self.args) < self.arity:
>            return self
>        else:
>            return self.func(*self.args)
>
>    __radd__ = __add__
>
> Infix = lambda func: InfixArity(2)(func)
>
> And of course, one can use __mul__ or __div__ or whatever to taste. "1
> // add // 2” doesn’t make me instantly vomit in my mouth. ;-)
>
> -- Carl Johnson
>