4.2.1.3. Option type support

These functions and predicates implement the standard library for working with option types. Note that option type support is still incomplete.

Option type support for Booleans

In this section: absent, deopt, occurs.

absent

predicate absent(var opt bool: x)

True iff x is absent

deopt

predicate deopt(var opt bool: x)

Return value of x (assumes that x is not absent)

occurs

predicate occurs(var opt bool: x)

True iff x is not absent

Option type support for integers

In this section: absent, deopt, had_zero, occurs.

absent

predicate absent(var opt int: x)

True iff x is absent

deopt

function var $$E: deopt(var opt $$E: x)

Return value of x (assumes that x is not absent)

had_zero

test had_zero(var opt int: x)
test had_zero(opt int: x)
test had_zero(array [int] of var opt int: x)

True if x had zero in its original domain.

Returns true if absent zero representation is disabled or if it is possible that \(\text{occurs}(x) \wedge \text{deopt}(x) = 0\)

occurs

predicate occurs(var opt int: x)

True iff x is not absent

Option type support for floats

In this section: absent, deopt, occurs.

absent

predicate absent(var opt float: x)

True iff x is absent

deopt

function var float: deopt(var opt float: x)

Return value of x (assumes that x is not absent)

occurs

predicate occurs(var opt float: x)

True iff x is not absent

Other declarations

In this section: absent, deopt, occurs.

absent

 test absent($T: x)

 test absent(var $T: x)

 test absent(set of $$T: x)

 test absent(var set of $$T: x)

 test absent(opt $T: x)

1-4.: Test if x is absent (always returns false)

Test if x is absent

deopt

 function $$T: deopt(opt $$T: x)

 function $T: deopt(opt $T: x)

 function array [$$U] of $$T: deopt(array [$$U] of opt $$T: x)

 function array [$$U] of $T: deopt(array [$$U] of opt $T: x)

 function var $T: deopt(var $T: x)

 function $T: deopt($T: x)

 function array [$U] of var $T: deopt(array [$U] of var $T: x)

 function array [$$U] of var bool: deopt(array [$$U] of var opt bool: x)

 function array [$$U] of var $$E: deopt(array [$$U] of var opt $$E: x)

 function array [$$U] of var float: deopt(array [$$U] of var opt float: x)

Return value of x if x is not absent. Returns undefined when evaluated on absent value.
Return value of x if x is not absent. Returns undefined when evaluated on absent value.

3, 4.: Return array of the value of x[i] where x[i] is not absent. Returns undefined when evaluated with an absent element.
5-7.: Return value x unchanged (since x is guaranteed to be non-optional).
8-10.: Return array of the value of x[i] (assumes that x[i] is not absent).

occurs

 test occurs($T: x)

 test occurs(var $T: x)

 test occurs(set of $$T: x)

 test occurs(var set of $$T: x)

 test occurs(opt $T: x)

1-4.: Test if x is not absent (always returns true)

Test if x is not absent