This mail is publicly posted to a distribution list as part of a process
of public discussion, any automatically generated statements to the
contrary non-withstanding. It is the opinion of the author, and does not
represent an official company view. (01)
Ed Barkmeyer wrote
> A program is a design for a machine, a set of instructions
> for assembling off-the-shelf parts into a machine that
> performs some function. Therefore, the primary concern of
> any programming language is to provide the ability to
> formulate a precise set of instructions for the assembly of
> useful machines. (02)
Ed, (03)
My perspective is that the aim of a programming language is to
allow the human to express the problem in terms a human can understand,
in order that they do not have to learn how to translate it into the
assembly code that the machine understands. This job is constrained in
two sorts of ways: firstly, the human needs to make the machine do what
the machine can do, and secondly, if the machine can't do it, the
translation process won't work. After that, the questions are about what
level of complexity the translator can cope with. (04)
A symbolic assembler gives the ability to formulate a precise
set of instructions. For portability, formula translation allowed
programmers to use familiar arithmetic notation, while language
implementers (compiler writers) sorted out the problem of converting the
formulae into precise sets of assembly instructions. (05)
Thus I would still assert that the primary aim of
<i>languages</i> is for humans to understand what they want the machine
to do, since there are other ways of getting the same result, but the
primary <i>constraint</i> is that languages must translate into a
precise set of instructions. (06)
Actually, the problem for languages is slightly harder than just
formulating a precise set of instructions. What we want is that the
program gives a precise result. Ideally, the same problem solved by two
different computer systems should give the same result. While this seems
to be the case with the algorithmic languages, I'm told that the various
logic solvers can give different results for the same set of inputs -
say, an OWL file. I'm not sure why this is the case, but comments
welcome. (07)
Sean Barker
Bristol, UK (08)
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