vector-ref - access an element of a vector
(import (rnrs)) ;R6RS
(import (rnrs base)) ;R6RS
(import (scheme r5rs)) ;R7RS
(import (scheme base)) ;R7RS
Returns the contents of element k of vector.
Returns a single value; an object from the vector.
(vector-ref '#(1 1 2 3 5 8 13 21) 5)
=> 8
(vector-ref '#(1 1 2 3 5 8 13 21)
(exact
(round (* 2 (acos -1)))))
=> 13
The specification of vectors does not actually require constant access time, but
in practice they are always implemented as flat arrays. Therefore this
procedure is used in algorithms that perform random-access operations on
arrays. Such algorithms would not have the same time complexity if lists were
used instead.
This procedure works the same everywhere.
This procedure can raise exceptions with the following condition types:
- &assertion (R6RS)
- The wrong number of arguments was passed or an argument was outside its
domain. In particular, k must be an exact nonnegative integer less
than the length of vector.
- R7RS
- The assertions described above are errors. Implementations may signal an
error, extend the procedure's domain of definition to include such
arguments, or fail catastrophically.
R4RS, IEEE Scheme, R5RS, R6RS, R7RS
This procedure first appeared in R2RS, where the vector notation was optional.