What is Expressiveness in a Computer Language

[Pascal Costanza]

Marshall wrote:
> Pascal Costanza wrote:
>> Consider a simple expression like 'a + b': In a dynamically typed
>> language, all I need to have in mind is that the program will attempt to
>> add two numbers. In a statically typed language, I additionally need to
>> know that there must a guarantee that a and b will always hold numbers.
> 
> I still don't really see the difference.
> 
> I would not expect that the dynamic programmer will be
> thinking that this code will have two numbers most of the
> time but sometimes not, and fail. I would expect that in both
> static and dynamic, the thought is that that code is adding
> two numbers, with the difference being the static context
> gives one a proof that this is so.

There is a third option: it may be that at the point where I am writing 
this code, I simply don't bother yet whether a and b will always be 
numbers. In case something other than numbers pop up, I can then make a 
decision how to proceed from there.

> In this simple example,
> the static case is better, but this is not free, and the cost
> of the static case is evident elsewhere, but maybe not
> illuminated by this example.

Yes, maybe the example is not the best one. This kind of example, 
however, occurs quite often when programming in an object-oriented 
style, where you don't know yet what objects will and will not respond 
to a message / generic function. Even in the example above, it could be 
that you can give an appropriate definition for + for objects other than 
numbers.


Pascal

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