QVT11 — MOF QVT 1.0, 8.2.2.22, Unclear specification of Unpack notation shorthand

Section 8.2.2.22 provides no guidance on the meaning of:

var x:X;
var y:Y;
var z:Z;
...
var (x:X,y,z) := self.foo();

[If one of the variables in the left hand side, does exist ...]

Possible interpretations

a) x:X is always a syntactical shorthand.

Therefore the above is a shorthand for:

var x:X;
var y:Y;
var z:Z;
...
var x:X; var (x,y,z) := self.foo();

and consequently there is duplicate variable definition to be
reported as a semantic error.

b) x:X is a convenience type check assertion

Therefore the above is a shorthand for:

var x:X;
var y:Y;
var z:Z;
...
var (x,y,z) := self.foo();

with a successful validation of type consistency.

c) x:X is not available as a shorthand

Therefore the above is a syntax error.

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Interpretations b) and c) require semantic knowledge to resolve syntactic
sugar.

Interpretation a) is an unambiguous syntax shorthand that could be more
clearly
described by:

"The following example demonstrates a shorthand in which variables are both
declared
and assigned.

var (x:X,y:Y,z) := self.foo();

Any variable name qualified by a type name is both a declaration and an
assignment,
with all declarations proceding the unapack assignment.
The above example should therefore be analyzed as:

var x:X; var y:Y; var (x,y,z) := self.foo();"

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Recommend interpretation a) with the above textual clarification.

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