World: r3wp

Tonight's Moment of REBOL Zen:

>> switch/default 'a [a 1] 2 
== 2

What's the insight here?

>> switch/default 'a [a [1]] 2
== 1

so what ?

Isn't it strange, that if the value being searched for (in this case 
a) is found, and the next item in the block isn't a block, then it 
fails to defaul?

No.

*default*

ok :)

From the docstring for SWITCH: "Selects a choice and evaluates the 
block that follows it."

>> switch 'a [a b [1]]
== 1
>> switch 'b [a b [1]]
== 1

must be a block, nothing else

Oh, the docs are different at
http://www.rebol.com/docs/words/wswitch.html
It sais "Selects a choice and evaluates what follows it."

Must be a block
 ... hm why?

because it says so

Ok, got it from Andreas' example. Multiple values. :)

C-style fallthrough.

(I think that was the intention behind that particular behaviour.)

yup, cute! :)

the syntax of switch evolved

it was different back...

Damn, now I have to change my own switch. ;)

Yes, I think back in 2.5 (or earlier), switch 'a [a 1] actually returned 
1.

Ah, that was still the case in 2.6, even.

I'm behind schedule, since I haven't noticed this.

2.7.2 it was:
http://www.rebol.net/upnews/0008.html

the change to switch was a good thing... wasn't it also mezz code 
a wee back?  IIRC this happened at the same time... and it made A 
LOT of code much faster.

>> - 2 + - 2
** Script error: - operator is missing an argument

is that in R3?

in R3, the - operator is not unary

or should we say, there is no unary version of the - operator?

That is false, actually

what is false?

what you wrote

in R2   -  can be either, no?

in R2, the - operator is both unary and binary, and its arity is 
determined during interpretation

so what is the diferrence in R3?

in R3, the - operator is not unary

well, that means there is only the binary version of the - operator.

that is false, as I see it

tell me how :


there is no unary version of the - operator  !=   the - operator 
is not unary

(I'm trying to understand what you mean... really)

1) There are not unary version and binary version of the - operator 
in R2, there is just one - operator in R2, which is both binary and 
unary depending on the "situation"

2) The statement "there is no unary version of the - operator" may 
be true only if you state, that NEGATE is not a unary version of 
the - operator

ok, well, to me the negate function is not an operator, but I understand 
what you mean.

I wrote: "...which is both binary and unary...", I could have written 
"...which is neither binary nor unary, since it does not have fixed 
arity, its arity being dependent on the situation..."

Would people miss unary minus in R3?

Ladislav, do you mean "fixed parity"?


And yes, there seem to be just one minus '-' in R2. If you redefine 
- with something like:
	set '- ...
, then you don't have unary minus any longer.

'Ladislav, do you mean "fixed parity"?' - no, I did mean "arity", 
not "parity"

And, in R2, the - operator is, in fact, variadic, having neither 
arity 1, nor 2

I learned some new words, thanks! :)

Would people miss unary minus in R3?

 - Initial testers reported its lack as a bug. The bug was dismissed, 
 since this was an intentional change. The benefits of the reduced 
 ambiguity won them over once they got used to it.

variadic
 - nice, I love precise words :)