Re: BKB's comments on AS

[Andrzej Tarlecki <tarlecki@mimuw.edu.pl>]

Dear Colleagues,

Just a brief comment from the semantics subgroup on the recently
emerging issue of a re-design of abstract syntax; I must add that i am
not sure how terribly relevant this is to the ongoing discussion and
comments from Bernd and Maura.

Anyway: from the semantic point of view, there are two kinds of
inclusions between various syntactic categories of the language.  One
is a true inclusion, were not semantic coercion is required, and the
meaning of a phrase in a subclass is exactly the same as the meaning
of this pohrase in a superclass. The other is when there is some
(usually quite obvious) semantic coercion involved: the meaning of a
phrased in a subclass is in some way modified to produce the meaning
of this phrase when considered in a superclass.

It would simplify considerably the semantics if these two kinds of
"inclusions" between syntatcic classes were distinguished in the
abstract syntax as well: the former would simply be an inclusion of
one syntactic category into another, the latter should require
preceding the phrases of the subcategory by some keyword.

Of course, this does not have to be preserved by the concrete syntax
at all.

Unfortunately, the final decisions on this will not be available until
the semantics is more or less ready --- and for this a more stable
design of the language must emerge from the current turmoil caused by
some discussions in Paris and Lille (soon, we all hope).

With best regards,

Andrzej