Fundamentals of CS I (CS151 2001S) : Reference

car: get the first element of a list

The Basics

Procedurecar
Parametersl, a list
PurposeExtracts the first element of a list.
ProducesThe first element of the list.
PreconditionsOne parameter (verified).
l is a list (verified).
l is nonempty (verified).
PostconditionsDoes not affect l.
Examples
> (car (cons 'a ()))
a
> (car (list 'c d e))
c
> (car 'a)
car: expects argument of type <pair>; given a
> (car ())
car: expects argument of type <pair>; given ()

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The source was last modified Sun Feb 4 10:45:07 2001.