Re: ARIANE-5 Failure (DC-X works)

[dewar@cs.nyu.edu (Robert Dewar)]

Samuel said

"Your definition misses a subtle distinction.  I can't define it
formally.  I think most of us view programmers as people who tell a
system HOW to do something.  The MatrixX user identifies WHAT to
compute, but not HOW."

The reason you cannot define this discinction formally is that it is
a meaningless one. That was the whole point of Lambert's point about
VHLANOS. One person's program is another persons abstract specification.

If I write:

  A := B * C + D * E;

that is (with minor notational differences) just a description of WHAT
should be done (compute a formula and put the result in A), not HOW
it should be done (i.e. I don't care about what instructions or
registers are used).

Sure the use of very high level languages like MatrixX raises this
to a higher level of abstraction, but you still cannot make any
meaningful discinction.

Now there are some related issues, e.g. whether you write in a procedural
style, but non-procedural languages have been around for at least 30
years (e.g. RPG!) and no one would claim that the use of a non-procedural
language means that you are not programming.

In Setl, if I say

  primes := { n in [2..100] | not exists d in [2 .. N - 1] | n mod d = 0};

that's essentially a mathematical definition of the set of primes from
2 to 100. If I look at it as an Ada programmer, it sure looks like a
specification and not a program, but it is in fact an executable Setl
program.

I simply don't believe you can succeed in drawing any meaningful
distinction between a program and an executable specification.