(quote (+ 1 2))
;; => (+ 1 2)
(quote nil)
;; => NIL
(quote blah)
;; => BLAH
(eval (quote (+ 1 2)))
;; => 3
(eval (quote blah))
;; ERROR!
(eval 1)
;; => 1
(eval nil)
;; => NIL
(eval T)
;; => T
(eval :blah)
;; => :BLAH
(eval (quote T))
;; => T
quote returns an expression as data. It prevents evaluation.
eval allows us to evaluate such data as an expression.
(list 1 2 3)
;; => (1 2 3)
(quote (1 2 3))
;; => (1 2 3)
'(1 2 3)
;; => (1 2 3)
quote provides an alternative way to create a list.
We can also use ' character to quote. This is an idiomatic way to create lists.
(setf my-list (quote (1 2 3)))
;; => (1 2 3)
(car my-list)
;; => 1
It's just a normal list!
(quote foo)
;; => FOO
'foo
;; => FOO
'(foo bar)
;; => (FOO BAR)
'((quote foo) (quote bar))
;; => ('FOO 'BAR)
As an alternative to using strings it's common to use quoted symbols.
(list (list 1) (list 2) (list 3))
;; => ((1) (2) (3))
'((1) (2) (3))
;; => ((1) (2) (3))
- quoted lists make it easier to read (and write) nested lists
(list (list (+ 1 1)) (list (+ 2 2)) (list (+ 3 3)))
;; => ((2) (4) (6))
'(((+ 1 1)) ((+ 2 2)) ((+ 3 3)))
;; => (((+ 1 1)) ((+ 2 2)) ((+ 3 3)))
- BUT nothing is evaluated inside a quoted list - it's all just data!
`((,(+ 1 1)) (,(+ 2 2)) (,(+ 3 3)))
;; => ((2) (4) (6))
- BUT you can use a quasiquoted list using the `` ` - the backtick character.
- Inside a quasiquoted list you can have evaluation toggled back on for a form by using the
,character. - It's QUASI!