Boolean Logic

Boolean values represent logical true and false, and are ubiquitous in computing.

Values and type

There are only two possible values of type BooleanType.

East type	Example value (JavaScript)	East object notation
`BooleanType`	`true`	`true`
`BooleanType`	`false`	`false`

Logical operations

East provides basic operations for manipulating Boolean values.

East function	Description	Example usage	Result
`Not`	Logical negation	`Not(true)`	`false`
`And`	Logical conjuction	`And(true, false)`	`false`
`Or`	Logical disjunction	`Or(true, false)`	`true`

Note that And and Or can accept multiple arguments for convenience. This is just a syntactical transformation. For example And(a, b, c) becomes And(a, And(b, c)) automatically (which only returns true when all three values are true).

If-else expressions

Computer programs execute different code depending on their inputs. One primary mechanism for this is "branching" into two different paths depending on whether a Boolean value is true or false. East provides the IfElse expression to perform this fundamental role.

East function	Description	Example usage	Result
`IfElse`	Logical branching	`IfElse(true, "a", "b")`	`"a"`

In imperative languages, the false (or else) branch of an if statement may be omitted. This is because in an imperative language, you can do something inside a code block. In a functional language like East, all an expression can do is produce a value, with no side effects. The IfElse expression must produce some value, whether the predicate was true or false. Thus, it is mandatory to include both branches.

Generating Boolean values with comparison

Boolean values are often generated by comparison – identifying whether a value is the same, greater than or less than another value. East provides operations Equal, NotEqual, Less, LessEqual, Greater and GreaterEqual for this purpose.

East function	Description	Example usage	Result
`Equal`	Determine if two values are equal	`Equal(1, 2)`	`false`
`NotEqual`	Determine if two values are not equal	`NotEqual(1, 2)`	`true`
`Less`	Determine if the first value is less than the second	`Less(1, 2)`	`true`
`LessEqual`	Determine if the first value is less than or equal to the second	`LessEqual(1, 2)`	`true`
`Greater`	Determine if the first value is greater than the second	`Greater(1, 2)`	`false`
`GreaterEqual`	Determine if the first value is greater than or equal to the second	`GreaterEqual(1, 2)`	`false`

You can compare values of any East type like, so long as both inputs are compatible (you cannot comare an integer and a string because they would never be equal). See the

tutorial on equality and ordering for more details.

Representation

Boolean values are represent as true and false in Elara's canonical JSON representation as well as East's object notation generated by Print.

Next steps

Continue to the next tutorial to understand how to use and manipulate integer and floating-point numbers with East and Elara.