- flexvector-index pred? fv1 fv2 ...procedure
Finds and returns the index of the first elements in fv1 fv2 ... that satisfy pred?. If no matching element is found by the end of the shortest flexvector, #f is returned. flexvector-index-right is similar, but returns the index of the last elements that satisfy pred?, and requires all flexvector arguments to have the same length. Given n arguments fv1 fv2..., pred? should be a function that takes n arguments and returns a single value, interpreted as a boolean.