PowerPoint Presentation - CS 60 Slides

first

lfirst returns the first element of a non-empty list:

lfirst([3, 5, 7, 11, 13]) ==> 3

lfirst([[3, 5, 7], 11, 13]) ==> [3, 5, 7]

lfirst([ ]) doesn’t make sense; it returns an error value

lBe sure that the argument to first is not [].