Maybe we don't need foreach ;-)

[Bill Baxter]

Walter Bright wrote:
> Bill Baxter wrote:
>> Just like some people have said, you can do everything with 'for'.
>> Well, actually maybe you can.  It occurred to me that foreach and for 
>> really don't clash.  One requires two semicolons, the other only one. 
>> So instead of a foreach we could have had
>>
>>   for(a; aggregate)
>>   {
>>
>>   }
> 
> That looks like a syntax error for one used to for loops.

For one used to C for loops, yes.  But Python for loops look like
   for a in aggregate: ...
Bash for loops look like
   for f in list; do ... done

There is certainly precedent for using 'for' synonymously with 'for each'.

>> or if the keyword 'in' had been used for the new construct instead of 
>> borrowing from c's ; syntax it would be:
>>
>>   for(a in aggregate)
>>   {
>>      ...
>>   }
> 
> 'in' is already an operator, so that wouldn't work.

It already has multiple duties as a storage type, so that alone 
shouldn't be an issue.
But I suppose you're right that it won't work here since a standard for 
loop can start with an Expression, which can contain an 'in'.  So this 
would require arbitrary lookahead to see if there are any ';''s coming 
or not.

Anyway, it wouldn't be a problem in a foreach :-).  foreach can only 
start with ForeachTypeList so there would be no problems with:

    foreach(a in aggregate) { }

as far as I can tell.

>> which could quite peacefully coexist with good-ole
>>
>>   for (int i=0; i<10; i++)
>>   {
>>   }
>>
>> Oh well.  Too much momentum behind foreach and foreach_reverse now, I 
>> suppose, to make such a simplification.
> 
> foreach is a fairly well understood term, I think it needs less 
> explanation than a variant on for.

Perhaps.  But we're talking about epsilon vs 2*epsilon in terms of the 
amount of explanation required.

One thing foreach has going for it is that it makes it feasible to 
replace the ';' with the 'in' keyword.  :-)

--bb