From: Eric Mahurin <eric_mahurin@...>
Date: 2005-08-05T00:29:55+09:00
Subject: Re: ruby-dev summary 26468-26661

--- Brian Schr�der <ruby.brian@gmail.com> wrote:

> On 04/08/05, David A. Black <dblack@wobblini.net> wrote:
> > Hi --
> > 
> > On Thu, 4 Aug 2005, [ISO-8859-1] Brian Schr�der wrote:
> > 
> > > [snip]
> > >
> > > Then why don't we use two different delimiters, e.g. (,)
> which would
> > > even unify with method declaration.
> > >
> > > { (a, b=12) a+b }
> > > is quite clear, and counting nesting parenthesis has to
> be done in any
> > > parser so this
> > >
> > > { (a=12, (b,c) = [1,2]) a+b**c }
> > > is also possible
> > 
> > However, { (a) } would be ambiguous. (I don't particularly
> mind living
> > without default values in blocks, but I think () wouldn't
> fly.)
> 
> One could disambiguate this the same way it is done with
> methods:
> 
> { () (a) }
>
> like in
> 
> def anonymus() (a) end

That doesn't sound bad and is consistent with "def".  But, it
does introduce a backwards incompatibility when you have "{ (a)
}" in existing code.

> or one could use a differnt pair of symbols, though I don't
> really like that.
> 
> { <a, b=12> a+b }

Definitely wouldn't work.  Take a look at this:

{ <a, b=12 >  a+b>2 }

Do you interpret it that way or this way:

{ < a, b=12>a+b >   2 }




Here is my proposal:

{ args : code }

Even if when you make the args : optional to preserve
compatibility, I think this would be parsable if you treat the
arg list (possibly with default expressions) like a normal
statment except that the delimiter is ":" instead of ";".  This
should work because an arg list is a syntactically valid
statement.  i.e.

a=1
other=[3,4]
a,b=2,*other

When the lexer finds a ":" instead of a ";" or newline as the
statement delimiter of first statement, it would treat that as
the arg list.

I like this because it gives the minimal amount of punctuation
for the arg list - one character as a delimiter.



		
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