Then what about: obj $isinstance Iterable or obj $isinstance$ Iterable or obj *isinstance Iterable or obj isinstance? Iterable These don't use the backtick charackter (wich on some setups even is a unicode char not from 7bit ascii). -panzi On 07/22/2010 01:17 AM, Chris Rebert wrote:

On Wed, Jul 21, 2010 at 3:37 PM, Dag Odenhall wrote:

...

It could help readability if binary (arity of 2) functions could be applied infix with some syntax. For example, borrowing from Haskell, the backtick could be reintroduced for this purpose.

Good examples for this are isinstance and hasattr:

if some_object `isinstance` Iterable: ... elif some_object `hasattr` '__iter__':

Already proposed (by me) and rejected by the BDFL:

http://mail.python.org/pipermail/python-ideas/2007-January/000054.html

Cheers, Chris

On 07/22/2010 01:17 AM, Chris Rebert wrote:

...

On Wed, Jul 21, 2010 at 3:37 PM, Dag Odenhall  wrote:

...

It could help readability if binary (arity of 2) functions could be applied infix with some syntax. For example, borrowing from Haskell, the backtick could be reintroduced for this purpose.

Good examples for this are isinstance and hasattr:

   if some_object `isinstance` Iterable:        ...    elif some_object `hasattr` '__iter__':

Already proposed (by me) and rejected by the BDFL:

http://mail.python.org/pipermail/python-ideas/2007-January/000054.html

On Wed, Jul 21, 2010 at 4:33 PM, Mathias Panzenböck wrote: Then what about: <snip>        obj *isinstance Iterable

How would the parser distinguish that from multiplication?

or        obj isinstance? Iterable

That would look odd for non-interoggative binary functions: z = x cartesianProduct? y

These don't use the backtick charackter (wich on some setups even is a unicode char not from 7bit ascii).

Not using backtick definitely makes the proposal more viable. (Personally I <3 backtick though.) Cheers, Chris

This can be done in Python today:

...

...

class Infix(object): ... def __init__(self, func): ... self.func = func ... self.arg1 = self.arg2 = self.not_set = object() ... ... def __radd__(self, arg1): ... self.arg1 = arg1 ... if self.arg2 is self.not_set: ... return self ... else: ... return self.func(self.arg1, self.arg2) ... ... def __add__(self, arg2): ... self.arg2 = arg2 ... if self.arg1 is self.not_set: ... return self ... else: ... return self.func(self.arg1, self.arg2) ... @Infix ... def add(one, two): ... return one + two ... @Infix ... def mul(one, two): ... return one * two ... @Infix ... def power(one, two): ... return one ** two ... 1 + add + 1 2 2 + mul + 2 4 3 + power + 3 27

Enjoy. -- Carl 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 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

Dag Odenhall writes:

...

This can be done in Python today:

Quoting myself from the original post:

It is already possible[1] to make infix functions, but the solution is a hack and requires functions to be marked as infix.

I don't see how “add a new punctuation character to the syntax in every place where this is to be used” is less of a hack. For reference you might want to read over the debates that preceded the introduction of ‘@’ to the language. There is *very strong* resistance to adding syntax that uses arbitrary punctuation characters. IMO that resistance is for good reason: punctuation beyond what Python already supports today rarely improves readability, and usually worsens it. -- \ “All television is educational television. The question is: | `\ what is it teaching?” —Nicholas Johnson | _o__) | Ben Finney