Block evaluation

Hi,

I try to evalute the following block, but it doesn't work. I allways  
got a error message.

| x y z |
x:= [ y:=1. z:=2. x+y. ] .  x value.  [] in UndefinedObject>>DoIt  
{[y := 1.  z := 2]}


Regards
Ulli


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Soory , of course it must be : x:= [ y:=1. z:=2. z+y. ] .  x value.
and this works.

But why can't I do this:
   x:= [ y:=1. z:=2. z+y. ] .
and evaluate it later?


Regards
Ulli


Am 18.12.2006 um 01:04 schrieb Ulrich Hermann:

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Il giorno lun, 18/12/2006 alle 01.04 +0100, Ulrich Hermann ha scritto:
> Hi,
>
> I try to evalute the following block, but it doesn't work. I allways  
> got a error message.
>
> | x y z |
> x:= [ y:=1. z:=2. x+y. ] .  x value.  [] in UndefinedObject>>DoIt  
> {[y := 1.  z := 2]}

That is not an error message, it's just what get's print out when you do
a PrintIt of the the first expression. Try doing a PrintIt of both
expressions, and you should get the right result.

        Giovanni

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Block evaluation

Hi Ulli,

I tried your code out in a workspace.
Here is what I discovered.

The original:

| x y z |
x:= [ y:=1. z:=2. x+y. ] .  x value.  
{[y := 1.  x := 2]  } .


Ah this is a cool bug.

As you probably know,
"[ anything ]" is an object called a block context
x:= [ anything ] . x value .
will print the value of "anything" in this case "nil"
since we have not defined it.

There is a typo (I believe) in your second line. I am
guessing you wanted to write.
x:= [ y:=1. z:=2. z+y. ] . x value.
which gives the result 3.
as it stands you are trying to add a number to a block
context which gives a DNU.

The last line is also interesting
Try
{ y:= 1 . z := 2 }
ans: " #(1 2)"

or
{[y := 1.  x := 2] value }" ans: #(2)"

or
{[y := 1.  x := 2]  } first value " 2"


The square brackets are causing the evaluation of "y
:= 1.  x := 2"
to be delayed until later. The thing that prints out
what is going on it being more cryptic than it needs
to be by not printing the contents of the block
context which you would have more immediately
recognized.

hth.

Yours in service, -- Jerome Peace









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