case statement semantic in kernel language

[Marko Zerdin]

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.