where clause

[spir]

On 03/07/2011 09:26 AM, Russel Winder wrote:
> On Sun, 2011-03-06 at 20:23 -0500, bearophile wrote:
> [ . . . ]
>
> I wonder if you may have misunderstood the reason for the where clause
> in functional languages such as Haskell and ML (usually OCaml).  In
> these languages the body of a function must be a single value-returning
> expression.  This means there has to be a separate clause for all the
> declarations of the single-assignment variables -- caveat the use of
> monads

I know about nothing of Haskel and ML languages, but in Lisp-like ones there 
are explicite forms for statement sequences (eg 'begin' form in Scheme). Also, 
numerous special forms are implicitely sequential (eg func def or cond in Lisp 
& Scheme), but not all (eg if). Thus, one can construct super-expressions in 
imperative-like style. But this is not considered good style, indeed.

>> do {
>>      auto r = map!(sqr)(items);
>> } where {
>>      int sqr(int x) pure nothrow {
>>          return x * x;
>>      }
>> }
>
> What's wrong with:
>
>          {
>            auto sqr = function int ( int ) { return x * x ; } ;
>            auto r = map ! ( sqr ) ( items ) ;
>          }
>
> Seems idiomatic and straightforward with less noise?

Right. But this does not make any distinction between logical sequence and 
construction sequence. A construction sequence can always, conceptually, be 
(re)composed into a single complex expression. Hope I'm clear ;-)
Logically, the above indeed reads: "r is a mapping of sqr on items, where sqr 
is...". Compare with:
	this.update();	// effect on state
	return this.filter(pred);

> [...]

[OT]
> PS  I have begun to dislike languages that use semi-colon as a statement
> terminator!  (It took me 4 attempts to get my two line example to
> compile :-((

(Why 4? There are only 2 ';' there.)
Lol! You're not the only one. 66% of my syntax errors are missing ';' (33% are 
using '=' instead of '==' in unittest asserts, even after years of python & Lua 
who inherited the same stupid operators).
See also: http://www.dwheeler.com/readable/sweet-expressions.html for an 
example of trying to get rid of () noise in Lisp.
Indented D would be a great language, visually: no more {} and ';'. Then, we 
could reuse {} for something else (eg set & aa literals, or template params). 
We would certainly find a nice use for ';'. Using '=' for equality and eg ':=' 
for assignment, D would then be close to perfect in terms of base syntax ;-).
[/OT]

Denis
-- 
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