Elisp: Equality Test

By Xah Lee. Date: 2021-12-04. Last updated: 2024-07-01.

Generic Equality Tests

equal

Check datatype and value are same.

This is the most generic and commonly used. Can be used for comparing

Two Symbols
Two Strings
Two Integers
Two Floats
Two List's contents

🛑 WARNING: comparing a integer number and floating number doesn't work. (equal 3 3.0) returns nil.

;; test if two values have the same datatype and value.

(equal 3 3) ;  t
(equal 3.0 3.0) ;  t

(equal 3 3.0) ;  nil. Because datatype doesn't match.

;; test equality of lists
(equal '(3 4 5) '(3 4 5))  ;  t
(equal '(3 4 5) '(3 4 "5")) ;  nil

;; test equality of strings
(equal "e" "e") ;  t

;; test equality of symbols
(equal 'abc 'abc) ;  t

eq

Check if is the same object. Good for comparing

Two Integers
Two Symbols
Check if two Sequence Type are of the “same address”.

;; work on symbols
(eq 'x 'x) ; t

;; work on integer
(eq 2 2) ; t

;; ------------

;; does not work for string
(eq "e" "e") ; nil

;; does not work for float
(eq 2.1 2.1) ; nil

;; does not work on lists having same items
(let ( aa bb )
  (setq aa '(3 4))
  (setq bb '(3 4))
  (eq aa bb))
;; nil

;; work on lists having same address
(let ( aa bb )
  (setq aa '(3 4))
  (setq bb aa)
  (eq aa bb))
;; t

eql

like eq but also return true for two “same” floating numbers with same sign.

(eql 1.1 1.1) ; t
(eql 0.0 -0.0) ; nil

Compare Numbers

=

Elisp: Compare Numbers, Equality

Compare String, Symbol

string-equal and others.

Elisp: String Comparison, Equality, Order

Compare Char

char-equal and others.

Elisp: Character Type

Test Inequality

Use not to negate equality test.

;; use “not” to invert equality
(not (equal 3 4)) ;  t