Node: Literal expressions, Next: , Previous: Variable references, Up: Primitive expression types


Literal expressions

quote <datum> syntax
' <datum> syntax
<constant> syntax

(quote <datum>) evaluates to <datum>. <Datum> may be any external representation of a Scheme object (see section see External representations). This notation is used to include literal constants in Scheme code. 


     (quote a)                              ==>  a
     (quote #(a b c))                       ==>  #(a b c)
     (quote (+ 1 2))                        ==>  (+ 1 2)

(quote <datum>) may be abbreviated as '<datum>. The two notations are equivalent in all respects. 

'a                                     ==>  a
     '#(a b c)                              ==>  #(a b c)
     '()                                    ==>  ()
     '(+ 1 2)                               ==>  (+ 1 2)
     '(quote a)                             ==>  (quote a)
     ''a                                    ==>  (quote a)

Numerical constants, string constants, character constants, and boolean constants evaluate "to themselves"; they need not be quoted. 

'"abc"                                 ==>  "abc"
     "abc"                                  ==>  "abc"
     '145932                                ==>  145932
     145932                                 ==>  145932
     '#t                                    ==>  #t
     #t                                     ==>  #t

As noted in section Storage model, it is an error to alter a constant (i.e. the value of a literal expression) using a mutation procedure like set-car! or string-set!.