World: r3wp

My original goal was not binary diffs, but diffing blocks.

you are right. I looked into it and it looks to be way too slow, 
so I'm trying another approach.

>> negate 2 + - 2
== 0
>> - 2 + - 2
== -4

Bug?

Isn't unary minus introducing a third semantic rule? Functions are 
prefix, operators are infix with precedence over functions. And then 
unary minus is prefix with precedence similar to operators?

w> - (2 + (- 2))
== 0
w> (- 2) + (- 2)
== -4

Question is, how would we read
- 2 + - 2

It does correctly I think, here is the trace log:
>> - 2 + - 2
Trace:  - (word)
Trace:  2 (integer)
Infix:  op (add)
Trace:  - (word)
Trace:  2 (integer)

I'm asking, if unary minus should work as if being defined like this:

>> set '- :negate

no,  AFAICT the unary minus is applied exactly like all operator 
precedence (from left to right).


negate and  "-"  do not have the same precedence, as you noted, so 
its normal for:
    >> negate 2 + - 2    
and
    >> - 2 + - 2
to give different results.

Ok, intensional then. I'm surprised.

You shouldn't old pal :-)

Is unary minus the only prefix thing, that has same precedence as 
operators?

:) Sometimes I feel, I have no clue about this language. ;)

actually, unary minus has an higher precedence than other ops

Functions with literal arguments works about the same.

>> f: func ['a] [probe a]
>> f 2 + 2
2
== 4

So f gets the value 2 in this example.

Complicated rules! ;)

because functions with literals stop the evaluation flow

yeah

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?