Re: [Caml-list] If OCaml were a car

[skaller <skaller@users.sourceforge.net>]

On Sun, 2007-08-19 at 22:30 +0200, Tom wrote:
> On 19/08/07, John Carr <jfc@mit.edu> wrote:
>         
>         OCaml has a badly designed syntax processed by a badly
>         implemented
>         parser feeding into a backend that generates poor error
>         messages.
>         All this makes the language hard to use.  
> 
> I would just like to know, what exactly do you think is badly
> designed, and what would be a better alternative? Mind that I am not
> defending OCaml's syntax here (I have grown accustumed to it, but I do
> not find it superb... probably...), I just think that all criticism
> should be constructive (that is, shut up unless you've got a better
> idea). 

I disagree with that: Most analysis is
and should be destructive. Understanding problems is the
precursor to constructing better solutions.

Ocaml has lots of syntactic issues. It has too many operators,
so that it is hard to remember their 'precedence'. Some are
very un-natural, for example:

	if e then e1 else e2

The thing is that 'else' has a different 'precedence' than 'then'.
So you can write:

	if e then e1 else a; b; c

and a,b,c are all executed if the condition is false, but you
cannot write:

	if e then a; b; c else ...

and similarly for let/in. So you need parentheses in the 'then' branch
to write a 'larger' expression, but you need parentheses around the
whole if/else to write a 'smaller' expression in the else 
branch ..

Furthermore, because of the decision that procedures
return unit, you can write:

	if e then p;

without the else, but only if p has type unit: the syntax is so
confused it doesn't know if it is functional/expression based
(in which case the else expression should be mandatory)
or procedural (in which case procedure calls should return void
to prevent the call being used as an argument to an application).

Felix procedures return void, and it provides

	if e then e1 else e2 endif  // an expression
	if e do 
		s1; s2; s3; 
	elif e1 then                // optional
		s4; s5; s6;
	else 			    // optional
		s7; s8; s9;
	done; 			    // a statement 

and in both cases the text of the branches can be
transparently swapped around. The cost is additional syntax
and the mandatory terminator. But if you don't like it
you can roll your own syntax .. as in Ocaml. For example
Felix also parses:

	if (x < 1) print "Less";
	else print "No"; // optional

if the "C" domain specific sublanguage syntax (DSSL csyntax) is loaded
(which it is by default). And if you like Python or Haskell you can
even write:

	if (x < 1) $$
		print "Less"
	else $$
		print "No"

[the $$ is ugly, but something is required to initiate indent mode]

Well it is NOT clear that all these alternatives are actually
a good idea, just as it is NOT clear that excess use of camlp4 is
a good idea. In my experience, using the language's raw syntax,
even if it has warts, is more or less mandatory if you want 
other people to be able to read your code.

Can Ocaml syntax be improved? Yes, but not much. Felix has:

	print$ "Hello" + " World";

which is stolen from Haskell and gets used a lot. Even if I can
implement that with camplp4 I wouldn't. I'd like to see $ in
the standard language: then I'd use it.

Every 'feature' of Ocaml syntax I hate I also love, 
for example:

	let f x = 
		blah
		blah
	in

WOOPS! I forgot a pre-condition .. 

	let f x = 
		if precond x then specialvalue else
		blah
		blah
	in

so I can add just one line without touching the rest 
of the code .. this is really cool!! .. so maybe the
weird if/then/else isn't so bad after all ... :)

-- 
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net