boolean

#boolean

##Syntax boolean

##Description The boolean type is used for values that are either true or false. These true-false values can be combined by various operators such as or and and.

##Example

    var success : boolean := false
    var continuing := true      % The type is boolean
    �
    success := mark >= 60
    continuing := success and continuing
    if continuing then �

##Details This type is named after the British mathematician, George Boole, who formulated laws of logic.

The operators for true and false are and, or, xor, =>, and not. For two true/false values A and B, these operators are defined as follows:

A and B is true when both are true A or B is true when either or both are true A xor B is true when either but not both are true A => B (A implies B) is true when both are true or when A is false not A is true when A is false

The and operator has higher precedence than or, so A or B and C means A or (B and C).

The operators or, and and => are short circuit operators. For example, if A is true in A or B, B is not evaluated.

##Details The boolean type can be used as an index to an array.

##Example Declaration of an array with boolean index.

    var a : array boolean of int
    a (false) := 10
    a (true) := 20

##Details The put and get semantics allow put's and get's of boolean values. true values will be output as "true" and false values will be output as "false". The only legal input values are "true" and "false", which are case sensitive.

##See also explicittruefalseconstant.html (which discusses the values true.html and false.html), precedence.html and expn.html (expression).