vector-index

[procedure] vector-index pred vec1 vec2 ...

[procedure] vector-index-right pred vec1 vec2 ...

[procedure] vector-skip pred vec1 vec2 ...

[procedure] vector-skip-right pred vec1 vec2 ...

SRFI-43: vector-index applies pred to each parallel elements of vec1 vec2 ..., from 0-th elements, and returns the first index where pred returns true (iteration ends at the shortest vector).

vector-index-right reverses the direction of application of pred. All vectors have the same length.

vector-skip and vector-skip-right reverses the meaning of pred.

The names are parallel to srfi-13?'s string-index, string-index-right, string-skip and string-skip-right, but note the order of arguments (string version takes a string first).