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