From: Christophe Grandsire <christophe.grandsire@...>
Date: 2005-10-13T22:57:04+09:00
Subject: Re: Default argument values for blocks

Selon Eric Mahurin <eric_mahurin@yahoo.com>:

>
> Anybody ever just consider making a new expression (or maybe
> RHS?) rule just for these default values such that "|" was not
> in this expression?  (...) in this or-less expression would
> still use the normal expression.  Wouldn't this solve the
> problem?  You'd just be forced to use (...) whenever you wanted
> to "|".  That doesn't seem so bad.
>
> ... { |a,b=1|2|a*b }   # b default: 1, code: 2|a*b
> ... { |a,b=(1|2)|a*b } # b default: (1|2), code: a*b
> ... { |a,b=1+2|a*b }   # b default: 1+2, code: a*b
>
> I don't see any ambiguity doing it this way.
>

Yacc does. Even the simple { |a,b=1| a*b } fails because Yacc treats it as { |
a,b=(1| a*b) }. And that *cannot* be solved in the current state of Yacc. The
problem is that there doesn't seem to be *any* solution that solves both this
problem and the problem of allowing bitwise or's in default arguments, short of
renaming the bitwise or, which would be such a compatibility break that it isn't
worth contemplating.

This is at least my understanding of the problem.
--
Christophe Grandsire.

http://rainbow.conlang.free.fr

It takes a straight mind to create a twisted conlang.