If a is an index type and b is any type, the type of arrays with indices in a and elements in b is written Array a b. An array may be created by the function array. The first argument of array is a pair of bounds, each of the index type of the array. These bounds are the lowest and highest indices in the array, in that order. For example, a one-origin vector of length 10 has bounds (1,10), and a one-origin 10 by 10 matrix has bounds ((1,1),(10,10)).

The second argument of array is a list of associations of the form (index, value). Typically, this list will be expressed as a comprehension. An association (i, x) defines the value of the array at index i to be x. The array is undefined (i.e. _|_) if any index in the list is out of bounds. If any two associations in the list have the same index, the value at that index is undefined (i.e. _|_). Because the indices must be checked for these errors, array is strict in the bounds argument and in the indices of the association list, but nonstrict in the values.

Not every index within the bounds of the array need appear in the association list, but the values associated with indices that do not appear will be undefined.