- array-expand array booleans nil axisprocedure
Returns an array with the same bounds as array except possibly along the axis dimension. Array is sliced along axis and the elements of booleans (a vector of boolean values) are used to decide where, if anywhere, nil is to be interpolated: if the corresponding boolean is #t, nil is interpolated, otherwise the next slice is incorporated. It is an error if the size of booleans is not to the extent of the axis dimension in the result. It is also an error if nil does not have the same bounds as a slice. (APL expand.)