equal

eq

E Functions

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equal

Determines whether two expressions are equal

(equal expr1 expr2 [fuzz]) 

Arguments

expr1

The expression to be compared.

expr2

The expression to compare with expr1.

fuzz

A real number defining the maximum amount by which expr1 and expr2 can differ and still be considered equal.

When comparing two real numbers (or two lists of real numbers, as in points), the two identical numbers can differ slightly if different methods are used to calculate them. You can specify a fuzz amount to compensate for the difference that may result from the different methods of calculation.

Return Values

T if the two expressions are equal (evaluate to the same value); otherwise nil.

Examples

Given the following assignments:

(setq f1 '(a b c)) 

(setq f2 '(a b c)) 

(setq f3 f2)

(setq a 1.123456) 

(setq b 1.123457)

Compare f1 to f3:

Command: (equal f1 f3)

T

Compare f3 to f2:

Command: (equal f3 f2)

T

Compare a to b:

Command: (equal a b)

nil

The a and b variables differ by .000001.

Compare a to b:, with fuzz argument of .000001:

Command: (equal a b 0.000001)

T

The a and b variables differ by an amount equal to the specified fuzz factor, so equal considers the variables equal.

Comparing the eq and equal Functions

If the eq function finds that two lists or atoms are the same, the equal function also finds them to be the same.

Any atoms that the equal function determines to be the same are also found equivalent by eq. However, two lists that equal determines to be the same may be found to be different according to the eq function.