2008-08-26
First of all, if you don't have a master degree in computer science,
and, if your specialization is not in computer languages design (i.e.
logics, mathematical formalism, some elements of computational
linguistics), then, you probably won't understand this post. However,
if you are bright, and have a open mind, then the views expressed post
can be meaningful or beneficial to you.
To begin, let me make it explicit that this post is about the concept
of syntax and semantics in computer languages. For example, are
computer languages defined by syntax and semantics? Does syntax and
semantics comprise the whole of a computer language? What is a
computer language? What is syntax, what is semantics? etc.
First, lets note few facts:
• there is no formal and universally accepted definition of what is
meant by “semantics”. There may be some, if so defined, they are
typically based on “models” over idealized, abstract hardware (i.e.
operations on values in storage; as in finite state machine).
• semantics is tied to syntax. There cannot be semantics without
syntax. We could conceptualize a semantic without any syntax, but this
is basically not done.
• a computer language, is typically mathematically defined as a set of
operations on a set of chars. This typical definition, covers
effectively just the syntax. (See
http://en.wikipedia.org/wiki/Formal_language)
in general, the study of design of computer languages as languages for
practical use, does not have much formal background. Typically, some
computer scientists (the real ones are properly known as
Mathematicians), create a lang that is LOSELY based on their idea of
some mathematical theory (such as lambda calculus, or other sub
branches of logic.) Lisp, prolog, haskell, apl are such examples. For
vast majority of langs, such as pascal, logo, C, C++, Java, perl, awk,
sh, python, php, ruby, tcl, basic, fortran,... etc, basically their
design, creation, are far removed from any mathematics. It is pretty
much a so-called “art”. Any dummy, can conceive and create a computer
language from scratch based on basically just his personal experiences
in using lang and intuition. This does not mean the lang will be
“bad”. In fact, most successful or widely used langs, results from
such personal creativity.
One of the question we want to ask is, what is a computer language? As
we know, formal methods, such as those based on automata, has nothing
to do with actual langs and is basically just the study of syntax. A
formal languages, of course does also have semantics, but that
semantics basically means transformation of strings. This sense is far
different from what mean by “semantics” in pop books that deal with
real langs (such as the the text book “Programming Languages:
Application and Interpretation”", by Shriram Krishnamurth).
The other question we want to ask, related to the above, is “what
exactly is a computer language?”. There is a popular, unconcious
belief, that a computer language is made up of syntax and semantics.
However, as we know from above, there are no formal definition on what
exactly is semantics that can be applied to computer languages in
daily use.
So, what is then, a computer language? Is there a formal definition
that makes Java, C, perl, lisp, as computer languages? The answer is
just no in our current state of mathematics.
Why is syntax far more important than whatever we intuitively
understood as “semantics”? Because, it is syntax that we actually see
and use in a computer lang, and it is syntax that drives the
development of semantics. When you design a language, you start with
syntax, coupled with some vague idea of what u want to happen, then,
once you wrote a compiler, then is semantics born.
another reason syntax is far more important can be seen from the
history of math notations. Tech geekers might think, notation doesn't
mean much except some convenience aspects. But if you are acquainted
in history of math notation, you'll know that notation largely drove
many development and directions of mathematics. Examples include
arabic numeral with decimal positional notation, symbols for variables
→ abstract algebra, matrix notation → linear algebra, some notations →
calculus. (notations, is somewhat like terminology, in that sometimes
the existance of a notation/terminology have huge impact from
awareness of the concept to major influence on thought of a subject.)
Xah
∑
http://xahlee.org/
☄
On Aug 25, 1:58 pm, "xah...@
gmail.com"
gmail.com> wrote:>>> Yes.
>> And one (hopefully last) question. Have you considered writing a lisp,
>> or other language, yourself without these irregularities?
>
> No. My knowledge and experience of parsers and compilers is basically
> zero. Say, below any studious person who just graduated from college
> with a computer science degree.
>
> I have some interest in parsers, so this year i started to read and
> learn tools about parsers. In particular, my interest in parsers is
> writing tools for text processing, in particular processing nestedsyntaxsuch as lisp and xml. I have no interest in compilers though.
>
> With the profileration of tools today... i probably can hackup a
> interpreter for some new language in say, perl. Even that will take me
> perhaps half a year or more, and when done, it'd be basically a
> useless toy.
>
> as for language'ssyntax, i do not find nestedsyntaxideal. I have
> been programing elisp as hobby on and off for 2 years. For all my love
> of uniformality, AI, functional programing, honestly i find the nestedsyntaxproblematic. (not counting lisp irregularity since the few lispsyntaxirregularity doesn't matter that much in practice).
>
> (i find nestedsyntaxproblematic for practical reasons. Namely,
> reading the source code and typing it. The other major reason that
> sting me as i start to write more complex programs, is that sequencing
> functions forces me into so much nesting (i.e. several nested mapcar).
> I have some detail in this article:
> “The Concepts and Confusions of Prefix, Infix, Postfix and Fully
> Nested Notations”
http://xahlee.org/UnixResource_dir/writ/notations.html
> )
>
> Recently i've been thinking, a idealsyntaxthat completely ditchs any
> form of nesting insyntax. That is, the source code is just a bunch
> of lines, each line is just a sequence of functions. For example,
> Mathematica's prefix notation “f@g@x” or postfix notation “x//g//f”,
> or unix pipe (e.g. “x | g | f”), and APL'ssyntaxis similar idea.
>
> The problem with such asyntaxis that it limits functions to one arg
> only. A solution might be that for any function that needs 2 or more
> args, the lang makes everything as list. But then, this means simple
> things like “1+2*3” becomes something like polish notation “[2 3] * 1
> +”, which is quite unreadable and unatural. APL solves it by allowing
> both binary and uninary functions ... but then i don't think that'd be
> a perfectsyntax.
>
> another train of thought i had recently, is that, i think all langs
> should have lisp's nestedsyntax(with no irregularities), then
> another layer on top of it, whatever it may be. This is how
> Mathematica'ssyntaxis, and i presume also liskell. Since all textual
> langs has a abstractsyntaxtree, and the nestedsyntaxis isomorphic
> to trees, so theoretically all langs could have a nestedsyntaxlike
> lisp's. I'm not sure how difficult this actually is to do, or how
> difficult for a existing lang to add such a layer. I guess its rather
> trivial in the context of compiler science, but i don't know much
> about parsers/compilers to be sure.
>
> if all lang support the pure nestedsyntax, then it will have a major
> impact on cross-lang understanding, usher practical major progress on
> programer's understanding of the role ofsyntaxin langs, and have
> major impact on language translation (aka compiling). (after all,
> theoretically, proper parser/compiler creates a AST in the parsing
> stage anyway. A pure nestedsyntaxcould be made as a explicit stage.
> That is, sugarsyntax→ nestedsyntax→ AST)
>
> btw, i have a question... are those AST created in the parsing process
> as some kinda explicit datatype? Wouldn't it be easy to print them out
> like lisp's nested paren?
>
> it is my wild guess, that the idea all or almost all languages will
> have a nestedsyntaxlike lisp (as a layer), might actually be a
> reality say in maybe 20 or 50 years.
>
> * * *
>
> as for interests, i have much more interest in perfecting my expertise
> in elisp, and learning Haskell, and learning a theorem proving lang
> such as coq to enhance my understanding in mathematical logic.
>
> I also have far more interest in many math subjects and geometry
> programing subjects. I have much existing projects to be done in
> geometry of plane curves, tiling theory, algorithmic mathematical art,
> surface theory, etc. (you can find these on my website)
>
> my interest in computational mathematics (computational logic,
> programing geometry) outshine my interest in programing langs or
> typical computer science issues. (am expert in programing geometry; am
> newbie in computational logic)
>
> Xah
> ∑
http://xahlee.org/
>
> ☄
