On Wed, 18 May 2005, Rob Kinyon wrote:
On 5/18/05, Stuart Cook <[EMAIL PROTECTED]> wrote:To summarise what I think everyone is saying, []-reducing an empty list yields either:
1) undef (which may or may not contain an exception), or 2) some unit/identity value that is a trait of the operator,
depending on whether or not people think (2) is actually a good idea.
I would think that the Principle of Least Surprise points to (1), given that the standard explanation of the [EMAIL PROTECTED] is eval join( '+', @x ) ...
I'd say the principle of least surprise points to (1); in the sense that $sum = [+] @x; would Just Work, etc.
I also have a vague sense that the 'identity' value for an operator might also be useful in other places in the compiler (enabling optimizations, etc). Providing it as a trait means that these 'other things' could work even with user-defined operators. (And leaving the trait undefined gives you the behavior (1), if that's what you want.)
--scott
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( http://cscott.net/ )
