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.. index:: optional(Optional)
.. _optional/1:
.. rst-class:: right
object
optional(Optional)
Optional term handling predicates. Requires passing an optional term (constructed using the optional object predicates) as a parameter.
| Availability:
| logtalk_load(optionals(loader))
| Author: Paulo Moura | Version: 1:7:0 | Date: 2019-11-26
| Compilation flags:
| static, context_switching_calls
| Dependencies: | (none)
| Remarks: | (none)
| Inherited public predicates: | (none)
.. contents:: :local: :backlinks: top
Public predicates
.. index:: is_empty/0 .. _optional/1::is_empty/0:
is_empty/0 ^^^^^^^^^^^^^^
True if the optional term is empty. See also the if_empty/1 predicate.
| Compilation flags:
| static
| Mode and number of proofs:
| is_empty - zero_or_one
.. index:: is_present/0 .. _optional/1::is_present/0:
is_present/0 ^^^^^^^^^^^^^^^^
True if the optional term holds a value. See also the if_present/1 predicate.
| Compilation flags:
| static
| Mode and number of proofs:
| is_present - zero_or_one
.. index:: if_empty/1 .. _optional/1::if_empty/1:
if_empty/1 ^^^^^^^^^^^^^^
Calls a goal if the optional term is empty. Succeeds otherwise.
| Compilation flags:
| static
| Template:
| if_empty(Goal)
| Meta-predicate template:
| if_empty(0)
| Mode and number of proofs:
| if_empty(+callable) - zero_or_more
.. index:: if_present/1 .. _optional/1::if_present/1:
if_present/1 ^^^^^^^^^^^^^^^^
Applies a closure to the value hold by the optional term if not empty. Succeeds otherwise.
| Compilation flags:
| static
| Template:
| if_present(Closure)
| Meta-predicate template:
| if_present(1)
| Mode and number of proofs:
| if_present(+callable) - zero_or_more
.. index:: if_present_or_else/2 .. _optional/1::if_present_or_else/2:
if_present_or_else/2 ^^^^^^^^^^^^^^^^^^^^^^^^
Applies a closure to the value hold by the optional term if not empty. Otherwise calls the given goal.
| Compilation flags:
| static
| Template:
| if_present_or_else(Closure,Goal)
| Meta-predicate template:
| if_present_or_else(1,0)
| Mode and number of proofs:
| if_present_or_else(+callable,+callable) - zero_or_more
.. index:: filter/2 .. _optional/1::filter/2:
filter/2 ^^^^^^^^^^^^
Returns the optional term when it is not empty and the value it holds satisfies a closure. Otherwise returns an empty optional term.
| Compilation flags:
| static
| Template:
| filter(Closure,NewOptional)
| Meta-predicate template:
| filter(1,*)
| Mode and number of proofs:
| filter(+callable,--nonvar) - one
.. index:: map/2 .. _optional/1::map/2:
map/2 ^^^^^^^^^
When the optional term is not empty and mapping a closure with the value it holds and the new value as additional arguments is successful, returns an optional term with the new value. Otherwise returns an empty optional term.
| Compilation flags:
| static
| Template:
| map(Closure,NewOptional)
| Meta-predicate template:
| map(2,*)
| Mode and number of proofs:
| map(+callable,--nonvar) - one
.. index:: flat_map/2 .. _optional/1::flat_map/2:
flat_map/2 ^^^^^^^^^^^^^^
When the optional term is not empty and mapping a closure with the value it holds and the new optional term as additional arguments is successful, returns the new optional term. Otherwise returns an empty optional term.
| Compilation flags:
| static
| Template:
| flat_map(Closure,NewOptional)
| Meta-predicate template:
| flat_map(2,*)
| Mode and number of proofs:
| flat_map(+callable,--nonvar) - one
.. index:: or/2 .. _optional/1::or/2:
or/2 ^^^^^^^^
Returns the same optional term if not empty. Otherwise calls closure to generate a new optional term. Fails if optional term is empty and calling the closure fails or throws an error.
| Compilation flags:
| static
| Template:
| or(NewOptional,Closure)
| Meta-predicate template:
| or(*,1)
| Mode and number of proofs:
| or(--term,@callable) - zero_or_one
.. index:: get/1 .. _optional/1::get/1:
get/1 ^^^^^^^^^
Returns the value hold by the optional term if not empty. Throws an error otherwise.
| Compilation flags:
| static
| Template:
| get(Value)
| Mode and number of proofs:
| get(--term) - one_or_error
| Exceptions:
| Optional is empty:
| existence_error(optional_term,Optional)
.. index:: or_else/2 .. _optional/1::or_else/2:
or_else/2 ^^^^^^^^^^^^^
Returns the value hold by the optional term if not empty or the given default value if the optional term is empty.
| Compilation flags:
| static
| Template:
| or_else(Value,Default)
| Mode and number of proofs:
| or_else(--term,@term) - one
.. index:: or_else_get/2 .. _optional/1::or_else_get/2:
or_else_get/2 ^^^^^^^^^^^^^^^^^
Returns the value hold by the optional term if not empty. Applies a closure to compute the value otherwise. Throws an error when the optional term is empty and the value cannot be computed.
| Compilation flags:
| static
| Template:
| or_else_get(Value,Closure)
| Meta-predicate template:
| or_else_get(*,1)
| Mode and number of proofs:
| or_else_get(--term,+callable) - one_or_error
| Exceptions:
| Optional is empty and the term cannot be computed:
| existence_error(optional_term,Optional)
.. index:: or_else_call/2 .. _optional/1::or_else_call/2:
or_else_call/2 ^^^^^^^^^^^^^^^^^^
Returns the value hold by the optional term if not empty or calls a goal deterministically if the optional term is empty.
| Compilation flags:
| static
| Template:
| or_else_call(Value,Goal)
| Meta-predicate template:
| or_else_call(*,0)
| Mode and number of proofs:
| or_else_call(--term,+callable) - zero_or_one
.. index:: or_else_fail/1 .. _optional/1::or_else_fail/1:
or_else_fail/1 ^^^^^^^^^^^^^^^^^^
Returns the value hold by the optional term if not empty. Fails otherwise. Usually called to skip over empty optional terms.
| Compilation flags:
| static
| Template:
| or_else_fail(Value)
| Mode and number of proofs:
| or_else_fail(--term) - zero_or_one
.. index:: or_else_throw/2 .. _optional/1::or_else_throw/2:
or_else_throw/2 ^^^^^^^^^^^^^^^^^^^
Returns the value hold by the optional term if not empty. Throws the given error otherwise.
| Compilation flags:
| static
| Template:
| or_else_throw(Value,Error)
| Mode and number of proofs:
| or_else_throw(--term,@nonvar) - one_or_error
Protected predicates
(none)
Private predicates
(none)
Operators
(none)
.. seealso::
:ref:`optional <optional/0>`