Emacs Lisp: Check Element Exist in List

member

(member x list)

Check if x is in list. If so, return a list starting with the first occurrence of object. Else return nil.

Comparison done using equal. [see Emacs Lisp: Test Equality]

(member "4" '("3" "4" "5")) ;; ("4" "5")

member-ignore-case

(member-ignore-case x list)

same as member, except that x should be a string, and comparison ignores letter-case.

(member-ignore-case "A" '("b" "a")) ; ("a")

memq

(memq x list)

Same as member, but comparison done using eq. Use this if all items are Symbols.

memql

(memql x list)

Same as member, but comparison done using eql.

Reference

• Lists (ELISP Manual)