Scheme built-in to check list containment

问题

In Python I can do "x in list" to see if the list contains x. Is there any equivalent built-in in Scheme to do this?

回答1:

The R5RS, and the R6RS standard library for lists define memq, memv, and member which can be used for that purpose.

回答2:

In PLT Scheme, one has

(member whatever list)
(memv whatever list)
(memq whatever list)

from the SRFI which use, respectively, equal?, eqv?, and eq? to test for equality. There are also a number of other library functions related to searching in lists:

PLT Scheme list reference

回答3:

(define (contains? l i)
  (if (empty? l) #f
      (or (eq? (first l) i) (contains? (rest l) i))))

回答4:

No, there is no list built-in predicate that will do that for you. It's extremely easy to define a lambda or a macro to do just that though.

来源：https://stackoverflow.com/questions/1869116/scheme-built-in-to-check-list-containment