What is Expressiveness in a Computer Language

[Pascal Costanza]

Torben Ægidius Mogensen wrote:
> Pascal Costanza <pc at p-cos.net> writes:
> 
>> Torben Ægidius Mogensen wrote:
>>
>>> On a similar note, is a statically typed langauge more or less
>>> expressive than a dynamically typed language?  Some would say less, as
>>> you can write programs in a dynamically typed language that you can't
>>> compile in a statically typed language (without a lot of encoding),
>>> whereas the converse isn't true.
>> It's important to get the levels right here: A programming language
>> with a rich static type system is more expressive at the type level,
>> but less expressive at the base level (for some useful notion of
>> expressiveness ;).
>>
>>> However, I think this is misleading,
>>> as it ignores the feedback issue: It takes longer for the average
>>> programmer to get the program working in the dynamically typed
>>> language.
>> This doesn't seem to capture what I hear from Haskell programmers who
>> say that it typically takes quite a while to convince the Haskell
>> compiler to accept their programs. (They perceive this to be
>> worthwhile because of some benefits wrt correctness they claim to get
>> in return.)
> 
> That's the point: Bugs that in dynamically typed languages would
> require testing to find are found by the compiler in a statically
> typed language.

Yes. However, unfortunately statically typed languages also reject 
programs that don't have such bugs. It's a tradeoff whether you want to 
spend time to deal with them or not.

> So whil eit may take onger to get a program thatgets
> past the compiler, it takes less time to get a program that works.

That's incorrect. See http://haskell.org/papers/NSWC/jfp.ps - especially 
Figure 3.


Pascal

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