Boolean Equivalence

rascal-0.40.17

Synopsis

The equivalence operator on Boolean values.

Syntax

Exp₁ <==> Exp₂

Types

//

Exp₁	Exp₂	Exp₁ <==> Exp₂
bool	bool	bool

Description

The equivalence operator on Boolean values defined as follows:

Exp₁	Exp₂	Exp₁ <==> Exp₂
true	true	true
true	false	false
false	true	false
false	false	true

Boolean operators have short circuit semantics: only those operands are evaluated that are needed to compute the result. However, in the case of the <==> operator both operands have to be evaluated to determine the result.

Note that the <==> operator backtracks over its arguments until it finds an evaluation that is true, unless there is none. Variable bindings that are the effect of matching operators in its arguments are not visible outside the scope of the <==>.

Examples

rascal>import IO;
ok
rascal>false <==> false;
bool: true
rascal>false <==> true;
bool: false

NOTE: We should add a more meaningful example of backtracking over <==> than this old one: (i <- [1,2]) <==> (j <- [1,2,3]); for ((i <- [1,2]) <==> (j <- [1,2,3])) println("true!"); (i <- [1,2] && (i % 2 == 0)) <==> (j <- [1,2,3] && (j % 3 == 0)) for ((i <- [1,2] && (i % 2 == 0)) <==> (j <- [1,2,3] && (j % 3 == 0))) println("true!");