[Python-ideas] Infix functions

[Steven D'Aprano]

On Sat, Feb 22, 2014 at 08:34:51PM +0100, Hannu Krosing wrote:

> Why not use multiple "operator characters" for user-defined infix
> operators, like postgreSQL does ?
> 
> a *% b ++ c *% (d *. e)

How would that work in Python? Give an example (a toy or pretend example 
is fine) for how I would define an operator ^& for ints.

> We could even define that the characters in the combined operator define
> precendece so the
> above could be written as

Who is "we"? The programmer of the module, or the Python core devs? In 
other words, are the precedences set once, in the language, or in each 
module that uses them?

If I import an object x from one module with precedences set one way, 
and an object y from another module with precedences set another way, 
and try to use them in the same expression, whose precedences win?

An unrelated thought: there are currently eight ASCII symbols used for 
non-comparison operators in Python: ~%^&*-+/ (did I miss any?). Of 
those, three can be used as unary operators ~-+ and so should not be 
allowed in the second position. So with eight symbols available in the 
first position, and five in the second, that gives us 40 new infix 
operators. But one of them ** is already used, so 39.

To my mind, 39 arbitrary infix operators is both too many and too few. 
Too many, because, really, who needs 39 new infix operators? Who will 
remember them all? But too few, because it means that when you want a 
new operator, you have to force it into one of those 39 (48 if you can 
re-use one of existing operators, 52 if you include comparison operators 
> >= < <= but not equality and inequality). For example, I'd like to use 
∪ and ∩ for set union and intersection, but instead those two operations 
get mapped to & and | and I can never remember which is which. I'd like 
to use operators such as ⊕ ⊗. But so long as Python operators are ASCII 
only, that cannot happen.

But then, I have a mathematics background. I'm having trouble thinking 
of examples outside of maths where I would want to define infix 
operators at all, instead of just using a method or function.


-- 
Steven