Arrays

The ALDOR solution is very elegant. It is based on the following features

• In ALDOR, one can write a function which returns a domain (or a category). Moreover, such functions can take categories, domains or elements among their arguments. So, if T is a domain, one can create a function Array such that Array(T) is a domain whose elements are arrays of elements from T.
• In ALDOR, one can define a domain, a category or a function in any scope.

Of course, we do not plan to implement such features in ALLCOT. But we would like to create arrays of any type in any scope of the source program. However, in order to make such arrays easy to translate into our intermediate language, we can restrict to fixed size arrays. For declaring a variable of an array type, let us modify the Type-rules as follows.

Type	$\longmapsto$	%
Type	$\longmapsto$	id
Type	$\longmapsto$	Array ( id , ArithmeticExpression )

where, in the third rule, id is meant to be a type and ArithmeticExpression is meant to be a positive integer. For initializing an array, we need to add a special form of RightValue, such that the RightValue-rules become

RightValue	$\longmapsto$	FunctionCall
RightValue	$\longmapsto$	ArithmeticExpression
RightValue	$\longmapsto$	BooleanExpression
RightValue	$\longmapsto$	[ RightValueSequence ]
RightValueSequence	$\longmapsto$	RightValue
RightValueSequence	$\longmapsto$	RightValueSequence , RightValue

Then, we need to read and overwrite an element in an array, which means accessing an element in an array. This can be done exactly like in an AttributeCall. Therefore, the following program fragment becomes syntactically valid

x: Array(Integer, 3) := [2,3,6];
i: Integer := 2;
x.i := 5;

Observe that this solution for arrays is coherent for the philosophy of ALLCOT and ALDOR. In fact, the ALLCOT Array can be viewed as a built-in domain constructor.