none() Function

Calls a rule or function that returns either true or false for each item in list by asking the question, "Do all items in this list yield false for this rule/function?" with the intent to discover if no items will yield true.

Parameters

none( predicate, list, context )

Returns

Boolean

Using the function

The following sections cover important details about the none() function.

Using the predicate parameter

In the predicate parameter of none(), enter fn!functionName or a!functionName to reference an expression function, or rule!ruleName to reference a rule.

Using the context parameter

The context parameter lets you pass fixed parameters that stay the same for each list item.

When the predicate parameter has more than two parameters, the context parameter provides the remaining ones. See Checking items with context for an example.

Understanding results

The none() function returns false as soon as the returned value of an evaluation yields true; otherwise, returns true.

Empty and null lists yield true.

Unsupported functions

The none() function doesn't support a!forEach() in rules that you use as the predicate.

Examples

The following examples demonstrate the none() function.

To experiment with examples, copy and paste the expression into an expression rule and click TEST RULE to see the output.

Checking items in a list

This example checks whether no items in a list are null or empty, using a!isNullOrEmpty as the predicate.

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none(
  a!isNullOrEmpty,
  {1, 2, null, 3, null, 4}
)

Returns false.

Checking items in an empty list

This example shows how none() behaves when the list parameter is empty.

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none(
  a!isNullOrEmpty,
  {}
)

Returns true.

Checking items with context

To help demonstrate how the context parameter works in looping expressions, let's look at an example.

Imagine you're building an expression that uses looping to analyze group membership in your application. You have four Group constants configured in the following ways:

The following expressions reference these constants to show how context works when checking items in a list.

Checking items in a list with context

This example uses the context parameter to pass a group into every evaluation of the predicate.

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none(
  a!isUserMemberOfGroup,
  {"user1", "user2", "user3"},
  cons!csaAdmins
)

Returns false when user1 and user3 are members of the group referenced by cons!csaAdmins. The a!isUserMemberOfGroup() function has 3 parameters: username, groups, and matchAllGroups. The none() list corresponds to username, and the list of values provided in the context parameter are used as the next two parameters, groups and matchAllGroups.

Checking items in a list with context for more than two parameters

This example checks whether no user in a list belongs to all groups in a set. It passes two context values into a!isUserMemberOfGroup, which takes more than two parameters.

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none(
  a!isUserMemberOfGroup,
  {"user1", "user2", "user3"},
  {cons!allGroups, true}
)

Returns false when user1 is a member of all the groups referenced in cons!allGroups. The a!isUserMemberOfGroup() function has 3 parameters: username, groups, and matchAllGroups. The none() list corresponds to username, and the list of values provided in the context parameter are used as the next two parameters, groups and matchAllGroups.

Checking all items in a list with context for more than two parameters which accept lists

This example uses merge() to pass list values through the context parameter, mapping each list to a predicate parameter.

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none(
  a!isUserMemberOfGroup,
  {"user1", "user2", "user3"},
  merge({cons!csaAdmins, cons!csaProfs}, {true, true})
)

Returns false when user1 is a member of the groups referenced in cons!csaAdmins and cons!csaProfs. The merge() function maps the list values to the correct parameters in this example.

Checking a list with a custom expression rule

This example checks whether no dates in a list are later than a reference date. It uses a helper rule, rule!isDateLater(value, referenceDate), which is defined as:

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ri!value > ri!referenceDate

Example filter:

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none(
  rule!isDateLater,
  {date(1950, 2, 3), date(1950, 6, 23), date(1950, 5, 2)},
  date(1950, 4, 7)
)

Returns false.

Feature compatibility

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