What is Expressiveness in a Computer Language

Pascal Bourguignon pjb at informatimago.com
Thu Jun 22 19:02:49 CEST 2006

"Marshall" <marshall.spight at gmail.com> writes:

> 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. 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.
> This thread's exploration of the mindset of the two kinds
> of programmers is difficult. It is actually quite difficult,
> (possibly impossible) to reconstruct mental states
> though introspection. Nonetheless I don't see any
> other way to proceed. Pair programming?

Well this is a question of data flow.  As I explained, there's a whole
body of functions that don't process concretely the data they get.
But of course, eventually you must write a function that do some
concrete processing on the data it gets.  That's when you consider the
type of the values. Such functions may be generic functions with
methods dispatching on the actual type of the parameters, or you may
encounter some TYPECASE or COND inside the function before calling
non-abstract "primitives" that work only on some specific type.

__Pascal Bourguignon__                     http://www.informatimago.com/

"I have challenged the entire quality assurance team to a Bat-Leth
contest.  They will not concern us again."

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