Subj : Re: Compiler and an interpreter
To   : comp.programming
From : Gerry Quinn
Date : Wed Aug 03 2005 01:00 pm

In article <42efa9d3$0$24029$ed2619ec@ptn-nntp-reader01.plus.net>, 
usenet@jdh30.plus.com says...
> Gerry Quinn wrote:
> >> For example, computing the maximum of 5 and each element of a list in
> >> OCaml:
> >> 
> >>   # List.map (max 5) [1;2;3;4;5;6;7;8;9];;
> >>   - : int list = [5; 5; 5; 5; 5; 6; 7; 8; 9]
> > 
> > And using simple iterative methods in C++ it's just as easy.
> 
> Do you honestly think the 13 lines of C++ are "just as easy" as the 1 line
> of OCaml? The gap between OCaml and C++ widens as programs get more
> complicated.

If you get 13 lines to make a copy of a list of ints with each replaced 
by the larger of 5 and the value in the original array (which I assume 
you are doing), you must be including curly brackets and various 
standard includes.

The guts of it might look something like:

list < int > copyList;
for ( list< int >::iterator it = origList.begin(); 
		it != origList.end(); it++ )
{
	copyList.push_back( max( *it, 5 ) );
}

Or are you worried about the definition of the specific list?  That can 
often be a little clumsy in C++.  But it's hardly much of a reason to 
choose between languages.  (Nor, indeed, is verbosity.  
Comprehensibility is most important.)

Of course, using a list as you do in Ocaml would likely be a grossly 
inefficient representation of this data compared to a vector, at least 
on typical PC architecture, since it may get scattered all over memory.

> For example, here's the OCaml code required to compute the set of
> "n"th-nearest neighbours in a periodic graph:

[-]

> Not only is the OCaml much shorter than the C++, it is also more robust
> thanks to static type checking, more maintainable thanks to better code
> reuse and 100x faster thanks to functional programming.

If indeed it is 100x faster, it is because you have written unidiomatic 
and slow C++, using libraries that are not designed for efficiency.  

I don't believe your benchmarks are valid.

I do accept that for the small subset of programming tasks that equate 
to implementing complex mathematical formulae, implementations that use 
functional languages will indeed tend to be more compact.  For what 
that is worth.

- Gerry Quinn

.