car

Documentation

;;; (car pair) -> any?
;;;   pair : pair?
;;; Grabs the first element of the pair.

Examples

> (car (cons 1 2))
1
> (car (cons "x" "y"))
"x"
> (car null)
. . car: contract violation
  expected: pair?
  given: '()

Tests

Forthcoming.

See also

car (for lists), cdr, cons

Questions

Why don’t you have an implementation of car?

car is a primitive procedure. It’s (nearly) impossible to implement it in terms of more basic operations.

Why are there two sets of documentation for car?

We initially learn car in terms of lists. When we start to learn about pairs, we also consider its meaning for those structures.