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Containers

Fabl introduces two kinds of parametric types which are not found in OWL: container types, and function types. Container types are described in this section. The container types are subclasses of the three container classes defined in RDF: rdf:Seq, rdf:Bag, and rdf:Alt.

For any Fabl type <Type>, SeqOf(<Type>) (resp BagOf(<Type>), AltOf(<Type>)) is the type of sequences (resp bags, alts) whose elements belong to <Type>. Sequences, Bags, and Alts behave identically in Fabl - only their intended meaning is different. (See the RDF documentation on containers). Sequences can be given by enclosing their members in brackets. For example.

var someIds = ['aa','bb','cc'];
someIds;
-->[aa,bb,cc]

The types of the bracketed expressions must match, so that for example,

[1,'a'];

will generate an error. However, since all data can be cast to Resource (see the section on type casting), this is not a limitation on the content of sequences, only on the expressions used to construct them.

[1~ob,'a'~ob]

is perfectly legal.

Bags and Alts are generated by expressions of the form bag(elt₀,elt₁ ... elt_n) or alt(elt₀,elt₁ ... elt_n) respectively. Example:

var bagOfInts = bag(1,2,3);

As for sequences, the types of elements must match.

To access elements of a container by index, conventional syntax is used, as illustrated by:

someIds[1];
-->bb
someIds[1] = 'abc';
someIds;
-->[aa,abc,cc]

Note that sequence selection is zero-based: s[0] is equivalent to s.rdf:_1

The following operations are available for all container types <tp>:

<tp> function new(Type <tp>)

returns an empty container of the given type tp. For example

new(SeqOf(int));

returns an empty sequence of ints.(new also manufactures new elements of OWL classes.)

<Type> function plus(<Type> x,<Type> y)

concatenates x and y of the same container type <Type>. As always, the operator + is equivalent to plus. Thus, for example:

[1,2,3] + [10,20,30] + [100];
-->[1,2,3,10,20,30,100]

plus does not modify its inputs, but, as for strings, times does.

<Type> function times(<Type> x,<Type> y)

adds the elements of y onto the end of x, and returns x. As always, the operator * is equivalent to times. Thus, for example:

var ss = [2,3,4];
-->[2,3,4,5,6]
ss * [5,6];
ss;
-->[2,3,4,5,6]

The following functions:

SeqOf(<Type>) function push(SeqOf(<Type>) x,<Type> y)

BagOf(<Type>) function push(BagOf(<Type>) x,<Type> y)

AltOf(<Type>) function push(AltOf(<Type>) x,<Type> y)

add y onto the end of x. For example:

var ss = [1,2];
push(ss,3);
->[1,2,3]
ss;
->[1,2,3]

void function reset(<Type> s)

resets the container s to zero length.

int function length(<Type> s)

returns the length of the container.