[Edu-sig] re: Types and true division (was Re: strange output)

[Danny Yoo]

> Only because Python is still young. Others have and I trust and hope
> many others will share that experience in the future.
>
> > And what would that side effect be?  What's the benefit >of 1/2==0?
>
> Provides the signal and the reminder of the importance of giving
> attention to the underlying numeric typing scheme.

Hello!

This model assumes that the programmer believes that division between
integers is possible.  *grin*


Seriously though, some other languages hold division as a very strict and
dangerous thing.  Standard ML, for example, takes its types darn
seriously: it doesn't even allow division between integers using '/'!

###
- 1.0 / 2.0;
val it = 0.5 : real
- ;
- ;
- 1 / 2;
stdIn:18.3 Error: overloaded variable not defined at type
  symbol: /
  type: int
- ;
- ;
- 1 div 2;
val it = 0 : int
- ;
- ;
- 1.0 div 2.0;
stdIn:23.5-23.8 Error: overloaded variable not defined at type
  symbol: div
  type: real
###

(SML's prompt character is '- ', which is visually confusing...)


ML'ers use a separate DIV operator that explicitely does truncation
between integers.  So that is one potential future that Python could have
turned toward, but all this typing does feel a bit like bondage.  If we
really want to teach typing concepts, I don't think Python's the language
to do this.

Should a programming languages abstract the numeric model of the machine
away from the programmer?  In the case of Python, it looks like the answer
is leaning toward "yes", especially since it already has long integers and
complex numbers (and probably rationals soon!) as basic types that the
programmer can use.


My feeling is that Python division doesn't have to reflect what the
machine is doing underneath.  At long as we explain to folks that Python
is an abstraction on top of the machine, I don't think it will cause
long-term harm.

The big problem is if we just use just Python alone to teach how computers
work: that would be an extraordinarily unbalanced view!  If we want to
show people the real details about computation, then we really should be
doing this in combination with a low-level language like MIPS assembly.
Have you thought about doing something like this?


Best of wishes to you!