What is Expressiveness in a Computer Language

[Joe Marshall]

Xah Lee wrote:
> in March, i posted a essay "What is Expressiveness in a Computer
> Language", archived at:
> http://xahlee.org/perl-python/what_is_expresiveness.html
>
> I was informed then that there is a academic paper written on this
> subject.
>
> On the Expressive Power of Programming Languages, by Matthias
> Felleisen, 1990.
> http://www.ccs.neu.edu/home/cobbe/pl-seminar-jr/notes/2003-sep-26/expressive-slides.pdf
>
> Has anyone read this paper? And, would anyone be interested in giving a
> summary?

The gist of the paper is this:  Some computer languages seem to be
`more expressive' than
others.  But anything that can be computed in one Turing complete
language can be computed in any other Turing complete language.
Clearly the notion of
expressiveness isn't concerned with ultimately computing the answer.

Felleisen's paper puts forth a formal definition of expressiveness in
terms of semantic
equivilances of small, local constructs.  In his definition, wholescale
program transformation is
disallowed so you cannot appeal to Turing completeness to claim program
equivalence.

Expressiveness isn't necessarily a good thing.  For instance, in C, you
can express the
addresses of variables by using pointers.  You cannot express the same
thing in Java, and
most people consider this to be a good idea.