Lists

 

• a list is an ordered set of elements (a 1 b ...)

• an element of a list can be a number, an identifier or another list, e.g., (a (2))

• empty list ( )

• selection operations

  • first returns the first element of a list: first[(a (2))] => a

  • second returns the second element of a list: second[(a (2))] => (2)

  • rest returns everything but the first element of a list: rest[(a (2))] => ((2))

• constructive operations

  • cons adds an element to the beginning of a list: cons[1, (a b)] => (1 a b)

  • list builds a list from its arguments: list[a, b] => (a b)