What is Expressiveness in a Computer Language

[Rob Thorpe]

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

In my experience the opposite is true for many programs.
Having to actually know the precise type of every variable while
writing the program is not necessary, it's a detail often not relevant
to the core problem. The language should be able to take care of
itself.

In complex routines it can be useful for the programmer to give types
and for the compiler to issue errors when they are contradicted.  But
for most routines it's just an unnecessary chore that the compiler
forces on the programmer.