.. index:: single: either .. _either/0:

.. rst-class:: right

object

either

Types and predicates for extended type-checking and handling of expected terms.

| Availability: | logtalk_load(expecteds(loader))

| Author: Paulo Moura | Version: 0:9:0 | Date: 2025-06-19

| Compilation flags: | static, context_switching_calls

| Provides: | :ref:`type::type/1 <type/0::type/1>` | :ref:`type::check/2 <type/0::check/2>` | :ref:`arbitrary::arbitrary/1 <arbitrary/0::arbitrary/1>` | :ref:`arbitrary::arbitrary/2 <arbitrary/0::arbitrary/2>` | :ref:`arbitrary::shrinker/1 <arbitrary/0::shrinker/1>` | :ref:`arbitrary::shrink/3 <arbitrary/0::shrink/3>` | :ref:`arbitrary::edge_case/2 <arbitrary/0::edge_case/2>` | Uses: | :ref:`expected <expected/0>` | :ref:`expected(Expected) <expected/1>` | :ref:`random <random/0>` | :ref:`type <type/0>`

| Remarks:

• Type-checking support: Defines a either(ValueType, ErrorType) type for checking expected terms where the value and error terms must be of the given types.
• QuickCheck support: Defines clauses for the type::arbitrary/1-2, arbitrary::shrinker/1, arbitrary::shrink/3, and arbitrary::edge_case/2 predicates to allow generating random values for the either(ValueType, ErrorType) type.

| Inherited public predicates: | (none)

.. contents:: :local: :backlinks: top

Public predicates

.. index:: expecteds/2 .. _either/0::expecteds/2:

expecteds/2 ^^^^^^^^^^^^^^^

Returns the values stored in the expected terms that hold a value.

| Compilation flags: | static

| Template: | expecteds(Expecteds,Values) | Mode and number of proofs: | expecteds(+list(expected),-list) - one

---

.. index:: unexpecteds/2 .. _either/0::unexpecteds/2:

unexpecteds/2 ^^^^^^^^^^^^^^^^^

Returns the errors stored in the expected terms that hold an error.

| Compilation flags: | static

| Template: | unexpecteds(Expecteds,Errors) | Mode and number of proofs: | unexpecteds(+list(expected),-list) - one

---

.. index:: partition/3 .. _either/0::partition/3:

partition/3 ^^^^^^^^^^^^^^^

Retrieves and partitions the values and errors hold by the expected terms.

| Compilation flags: | static

| Template: | partition(Expecteds,Values,Errors) | Mode and number of proofs: | partition(+list(expected),-list,-list) - one

---

.. index:: sequence/2 .. _either/0::sequence/2:

sequence/2 ^^^^^^^^^^^^^^

Returns an expected term with a list of all values when all expected terms hold values. Otherwise returns the first expected term holding an error.

| Compilation flags: | static

| Template: | sequence(Expecteds,Expected) | Mode and number of proofs: | sequence(+list(expected),--nonvar) - one

---

.. index:: traverse/3 .. _either/0::traverse/3:

traverse/3 ^^^^^^^^^^^^^^

Applies a closure to each list element to generate expected terms and then sequences them into a single expected term holding all values or the first error.

| Compilation flags: | static

| Template: | traverse(Closure,Terms,Expected) | Meta-predicate template: | traverse(2,*,*) | Mode and number of proofs: | traverse(+callable,+list,--nonvar) - one

---

Protected predicates

(no local declarations; see entity ancestors if any)

Private predicates

(no local declarations; see entity ancestors if any)

Operators

(none)

.. seealso::

:ref:`expected <expected/0>`, :ref:`expected(Expected) <expected/1>`, :ref:`type <type/0>`, :ref:`arbitrary <arbitrary/0>`