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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Time we switched to unicode? (was Explanation of this Python language feature?)
Date: Wed, 26 Mar 2014 00:30:21 -0400
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On 3/25/2014 8:12 PM, Steven D'Aprano wrote:
> On Tue, 25 Mar 2014 19:55:39 -0400, Terry Reedy wrote:
>
>> On 3/25/2014 11:18 AM, Steven D'Aprano wrote:
>>
>>> The thing is, we can't just create a =E2=88=91 function, because it d=
oesn't
>>> work the way the summation operator works. The problem is that we wou=
ld
>>> want syntactic support, so we could write something like this:
>>>
>>>       p =3D 2
>>>       =E2=88=91(n, 1, 10, n**p)
>>
>> Of course we can. If we do not insist on separating the dummy name fro=
m
>> the expression that contains it. this works.
>>
>> def sigma(low, high, func):
>>       sum =3D 0
>>       for i in range(low, high+1):
>>           sum +=3D func(i)
>>       return sum
>
> There is no expression there. There is a function.
>
> You cannot pass an expression to a function in Python,

One passes an unquoted expression in code by quoting it with either=20
lambda, paired quote marks (Lisp used a single '), or using it in a form =

that implicitly quotes it (that includes def statements). Unquoted=20
expressions in statements ultimately get passed to an internal functions.=


 > not in the sense I am talking about,

well, if you eliminate all the possibilities ...

 > because expressions are not first-class objects.

The concept is not a class, and the Python stdlib does not have an=20
expression class. But people have written classes to represent the=20
concept. I used existing classes instead.

Expressions are not (normally) mathematical objects either.
(An exception is rewriting theory, or other theories, where strings=20
representing expressions or WFFs (well-formed formulas) are the only=20
objects.) Mathematicians quote expression strings by context or=20
positiion. The sigma form is one of many examples.

--=20
Terry Jan Reedy