Land of Lisp - Ch 3

TL;DR

• code and data mode
• cons cells
• making lists using cons, ' and list

> (cons 1 ())
(1)
> (cons 1 (cons 2 ()))
(1 2)

> '(1 2)
(1 2)

> (list 1 2)
(1 2)

• car and cdr

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Chapter 3

Code and Data Mode

> (expt 2 3)    ; code mode
8

> '(expt 2 3)   ; data mode
(expt 2 3)

Lists

Using cons to create lists

> (cons 'chicken 'egg)
(CHICKEN . EGG)

> (cons 'chicken 'nil)
(CHICKEN)

> (cons 'chicken ())
(CHICKEN)

> (cons 'chicken '(egg omlette))
(CHICKEN EGG OMLETTE)

Using car and cdr

These work up to 4 levels deep. Anything deeper (e.g. cadadar) you'll have to write yourself. Also note that it works from back to front (look at caddr for example)

> (car '(1 2 3 4 5))
1
> (cdr '(1 2 3 4 5))
(2 3 4 5)
> (cadr '(1 2 3 4 5))
2
> (cddr '(1 2 3 4 5))
(3 4 5)
> (caddr '(1 2 3 4 5)) ; processes in this order -> d.. d.. a
3
> (car '( (1 2) 3 4 5)) ; using a nested list
(1 2)

Creating a list, threeways... (cons and list)

> (cons 'chicken (cons 'egg (cons 'omlette ())))
(CHICKEN EGG OMLETTE)

> (list 'chicken 'egg 'omlette)
(CHICKEN EGG OMLETTE)

> '(chicken egg omlette)
(CHICKEN EGG OMLETTE)

> '(cat (duck bat) ant)
(CAT (DUCK BAT) ANT)