From: Paul Lutus <nospam@...>
Date: 2006-09-11T11:45:22+09:00
Subject: Re: Struggling with Blocks

Logan Capaldo wrote:

> On Mon, Sep 11, 2006 at 07:45:28AM +0900, Paul Lutus wrote:
>> There is a need for both "do" and "begin" blocks. There is a need to
>> distinguish syntactically between a block that must be fed with items,
>> and one that must not be fed with items. To combine "do" and "begin"
>> would lead to syntactical ambiguity ... and surely then someone would ask
>> why the two purposes of "do" were not more clearly distinguished in the
>> syntax.
>> 
>> If "do" and "begin" were to be merged, it would be a little like the
>> ambiguous use of "<<" in C++. In one context, it shifts bits:
>> 
>> int x = 1,y;
>> 
>> y = x << 4; // y = 16
>> 
>> In another context, "<<" inserts items into a stream:
>> 
>> iostream x;
>> bool y;
>> 
>> y = x << 4; // y = true if the operation was successful
>> 
>> See the problem? Without my clear declarations directly above each case,
>> you would have a hard time distinguishing cases that use the same syntax.
>> This would make program listings hard to interpret and debug (a fact in
>> C++).
>> 
>> The multiple uses of "<<" in C++ is a well-known example, but the point I
>> am making is that it's important to avoid ambiguous syntax in language
>> design. "do ... end" always has a stream, and when the stream is
>> exhausted, the block exits. "begin ... end" never has a stream. It's easy
>> to remember and easy to read.
>> 
>> The end result of responding to every request for creative syntax
>> variations is called ... umm ... "Perl". :)
>> 
> Excellent argument, poor choice of example code *cough*.

Second reply, after reflection. Okay, I think you are saying the example
isn't very good because Ruby has the same ambiguity. Perhaps Matz didn't
want to leave C++ converts without any familiar landmarks?

-- 
Paul Lutus
http://www.arachnoid.com