case statement semantic in kernel language

[Peter Van Roy]

Dear Marko,

I think you are confusing the 'full' case statement with the 'kernel' 
case statement.
The 'kernel' case statement matches only a single record; its semantics 
is given on
page 67.  The 'full' case statement can have nested records (like in 
exercise 6 on
page 108); on pages 82-83 it is explained how to translate full case 
statements into
kernel case statements.

The definition of 'determined' is given in several places.  Briefly, a 
variable is
determined if it is bound to a number, procedure, or record.  A formal 
definition
is given on page 791.  From this definition it is clear that the 
record's arguments
can be unbound variables.

So I do think that the kernel language is completely formally defined in 
the book,
and certainly in sufficient detail to be implemented independently!

Best regards,

Peter



Marko Zerdin wrote:

> Hello.
>
> First, let me thank Peter and Seif for a great book, and all Oz gurus 
> for this most amazing language that you created. Second, I want to 
> apologize for posting this question here. It is strictly the book 
> question, but I wasn't certain where else to post it.
>
> In CTMCP, I've noticed a puzzling incompleteness of the case statement 
> semantic (on page 67) while trying to solve some of the exercises. I'm 
> sure I'm missing something somewhere along the way, so I would 
> appreciate it if somebody could follow through with my reasoning and 
> point to me what's wrong with it.
>
> First, the book says that the activation condition is true if the test 
> expression is determined, but doesn't specify what exactly 
> "determined" is supposed to mean in this case. Based on the observed 
> semantic of the case statement (clearly demonstrated by exercise 
> 2.6),  the expression does not need to be fully determined for the 
> option to be chosen (second case), but knowing only the record label 
> and arity is also not enough, which is what would follow from semantic 
> description. So what exactly is the activation condition?
>
> Second, according to the semantic on page 67, the alternative to be 
> taken is decided solely based on both expressions' record label and 
> arity, which is quite obviously not at all what is actually happening. 
> Let us assume that the label and arity both match, and therefore the 
> alternative is chosen. The interpreter is supposed to create a new 
> environment now, binding the values of all features in both records. A 
> few fundamental questions remain unanswered: What happens at the point 
> of creation of the new environment if one of the bindings fails? As an 
> alternative answer to the previous question, how exactly and when are 
> the bindings performed, and how exactly do they influence the 
> alternative selections process? The alternative is surely not 
> determined solely based on record label and arity, so how exactly is 
> it determined?
>
> I understood from the book that the kernel language definition is 
> supposed to be complete and should be simple enough to be implemented 
> independently for pedagogical purposes. However, I'm quite certain 
> that no such implementation could be done based solely on the 
> information that can be found in the book. Therefore, I would really 
> appreciate if you could give a full semantic of the case statement 
> upon which a determined and compatible implementation of the kernel 
> language could be based.
>
> Kind regards,
>
> Marko Zerdin.