Re: optional argument behavior

[Justin Walker <justin@mac.com>]

On Feb 1, 2005, at 12:18, Igor Schein wrote:

> Hi,
>
> Since I'm not sure whether it's a bug or a feature, I'm posting it
> here instead of reporting a bug:
>
> ? f(a,b=a)=[a,b]
> ? f(1)
> [1, a]
>
> For a very long time I've operated under ( a possibly false )
> assumption that the correct answer here would be [1, 1]

I'll take a leap of imagination and say that, in
   f(a,b=a)=....

the first 'a' is a formal argument (variable name), while the second 
instance will be assumed to come from the environment (at this point in 
the parsing, the formal variable 'a' has no existence).

Since (presumably) you have nothing in your environment named 'a', the 
assignment "b=a" will assign the symbol "a" to the formal argument 'b' 
if no value is provided in a call.

Sounds like a feature.

Cheers,

Justin

--
Justin C. Walker, Curmudgeon-At-Large  *
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