From: Logan Capaldo <logancapaldo@...>
Date: 2006-09-11T08:48:35+09:00
Subject: Re: Struggling with Blocks

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*.

a = 1 #=> 1
a << 1 #=> 2
$stdout << 4 # outputs '4'