Function

none( predicate, list, context )

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

Returns

Boolean

Usage considerations

Referencing expressions and rules

Use fn!functionName or a!functionName to reference an expression function and rule!ruleName to reference a rule.

Using rules or functions with multiple arguments

To use rules or functions that take more than two arguments, use the merge() function. For example, given a rule g(x, y, z), reduce(rule!g, i, merge({a, b, c}, {d, e, f})) returns g(g(g(i, a, d), b, e), c, f).

Understanding results

Returns false as soon as the returned value of an evaluation yields true; otherwise, returns true.

Empty and null lists yield true.

Limitations

a!forEach() cannot be used within rules used in this function.

Examples

Generalized behavior

Given a function f(x), none(fn!f, {a, b, c}, v) returns not(or({f(a, v), f(b, v), f(c, v)}))

Checking items in a list

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

Returns false.

Checking items in an empty list

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

Checking items in a list with context

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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. a!isUserMemberOfGroup 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 & matchAllGroups.

Learn more about a!isUserMemberOfGroup().

Checking items in a list with context for more than 2 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. a!isUserMemberOfGroup 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 & matchAllGroups.

Learn more about a!isUserMemberOfGroup().

Checking all items in a list with context for more than 2 parameters which accept lists

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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.

Learn more about a!isUserMemberOfGroup().

Checking a list with a custom expression rule

In this example, we will use 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