either — Logtalk 3.100.1

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:
type::type/1
type::check/2
arbitrary::arbitrary/1
arbitrary::arbitrary/2
arbitrary::shrinker/1
arbitrary::shrink/3
arbitrary::edge_case/2
Uses:
expected
expected(Expected)
random
type
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)

## Public predicates

### `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`

### `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`

### `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`

### `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`

### `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)

See also

expected, expected(Expected), type, arbitrary