object

optional

Constructors for optional terms. An optional term is either empty or holds a value. Optional terms should be regarded as opaque terms and always used with the optional/1 object by passing the optional term as a parameter.

Availability:
logtalk_load(optionals(loader))
Author: Paulo Moura
Version: 2:1:0
Date: 2021-01-03
Compilation flags:
static, context_switching_calls
Provides:
type::type/1
type::check/2
Remarks:

  • Type-checking support: This object also defines a type optional for use with the type library object.

Inherited public predicates:
(none)

Public predicates

empty/1

Constructs an empty optional term.

Compilation flags:
static
Template:
empty(Optional)
Mode and number of proofs:
empty(--nonvar) - one

of/2

Constructs an optional term holding the given value.

Compilation flags:
static
Template:
of(Value,Optional)
Mode and number of proofs:
of(@term,--nonvar) - one

from_goal/3

Constructs an optional term holding a value bound by calling the given goal. Returns an empty optional term if the goal fails or throws an error.

Compilation flags:
static
Template:
from_goal(Goal,Value,Optional)
Meta-predicate template:
from_goal(0,*,*)
Mode and number of proofs:
from_goal(+callable,--term,--nonvar) - one

from_goal/2

Constructs an optional term holding a value bound by calling the given closure. Returns an empty optional term if the closure fails or throws an error.

Compilation flags:
static
Template:
from_goal(Closure,Optional)
Meta-predicate template:
from_goal(1,*)
Mode and number of proofs:
from_goal(+callable,--nonvar) - one

from_generator/3

Constructs optional terms with the values generated by calling the given goal. On goal error or failure, returns an empty optional.

Compilation flags:
static
Template:
from_generator(Goal,Value,Optional)
Meta-predicate template:
from_generator(0,*,*)
Mode and number of proofs:
from_generator(+callable,--term,--nonvar) - one_or_more

from_generator/2

Constructs optional terms with the values generated by calling the given closure. On closure error or failure, returns an empty optional.

Compilation flags:
static
Template:
from_generator(Closure,Optional)
Meta-predicate template:
from_generator(1,*)
Mode and number of proofs:
from_generator(+from_generator,--nonvar) - one_or_more

Protected predicates

(no local declarations; see entity ancestors if any)

Private predicates

(no local declarations; see entity ancestors if any)

Operators

(none)

See also

optional(Optional), type