Comparison Operators

The comparison operators test whether one operand is the same as the other, or whether, if they can be ordered, they are ordered in a given direction. The result is a boolean.

The nature of comparisons involving strings can be influenced by a considering clause; see Chapter 19.

Lists are internally ordered, but records are not:

{1, 2} = {2, 1} -- false
{name:"Matt", age:"51"} = {age:"51", name:"Matt"} -- true

The equality (=) and inequality (≠) operators do not coerce their operands; operands may be of any datatype, and operands of different datatypes are unequal. So:

{"2"} = 2 -- false

In that example, the first operand is a list, the second operand is a number, and no coercion takes place. So the operands are not equal, and the comparison is false.

With the other comparison operators , operands must ultimately be a string, a number, or a date. The first operator is coerced to a string, a number, or a date, and then the second operator is coerced to match the datatype of the first:

{"2"} ≥ 2 -- true

In that example, the first operand is a list of one string, so it is coerced to a string. Now the second operand is coerced to a string; the two strings are equal and the comparison is true.

Thus, although you cannot use the equality operator to learn whether two values would be equal if implicitly coerced to the same datatype, you can work around the problem like this:

{"2"} ≤ 2 and {"2"} ≥ 2 -- true

As noted in "Assignment and Retrieval" in Chapter 7, the equality operator is not overloaded as an assignment operator. This code will compile and run, but it won't assign 4 to x (it will report whether they are equal):

x = 4