Result is the absolute value of Number, and of the same type.
This predicate can be used as a function in arithmetic expressions. In coroutining mode, if Number is uninstantiated, the call to abs/2 is delayed until this variable is instantiated.
Result is abs(1). % gives Result = 1
Result is abs(-5). % gives Result = 5
Result is abs(-6.2). % gives Result = 6.2
Result is abs(-0.6__-0.5). % gives Result = 0.5__0.6
Result is abs(-0.2__0.1). % gives Result = 0.0__0.2