What is Expressiveness in a Computer Language

[Pascal Costanza]

Neelakantan Krishnaswami wrote:
> In article <4fb97sF1if8l6U1 at individual.net>, Pascal Costanza wrote:
>> 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 ;).
> 
> This doesn't seem obviously the case to me. If you have static
> information about your program, the compiler can use this information
> to automate a lot of grunt work away.
> 
> Haskell's system of typeclasses work this way. If you tell the
> compiler how to print integers, and how to print lists, then when you
> call a print function on a list of list of integers, then the compiler
> will automatically figure out the right print function using your base
> definitions. This yields an increase in Felleisen-expressiveness over
> a dynamically typed language, because you would need to globally
> restructure your program to achieve a similar effect.
> 
> More dramatic are the "polytypic" programming languages, which let you
> automate even more by letting you write generic map, fold, and print
> functions which work at every type.

Yes, but these decisions are taken at compile time, without running the 
program.


Pascal

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