Clarify predicate function and empty list behavior (#1197)

Author: JPryce-Aklundh

modules/ROOT/pages/functions/predicate.adoc

@@ -54,6 +54,7 @@ CREATE
 .Considerations
 |===
 | `null` is returned if the `list` is `null` or if the `predicate` evaluates to `null` for at least one element and does not evaluate to false for any other element.
+| `all()` returns `true` if `list` is empty because there are no elements to falsify the `predicate`.
 |===
 
 .+all()+
@@ -86,6 +87,23 @@ image::predicate_function_example.svg[width="300",role="middle"]
 
 |===
 
+.`all()` on an empty `LIST`
+[source, cypher]
+----
+WITH [] as emptyList
+RETURN all(i in emptyList WHERE true) as allTrue, all(i in emptyList WHERE false) as allFalse
+----
+
+.Result
+[role="queryresult",options="header,footer",cols="2*<m"]
+|===
+| allTrue | allFalse
+
+| TRUE  | TRUE
+
+2+d|Rows: 1
+|===
+
 ======
 
 
@@ -106,6 +124,7 @@ image::predicate_function_example.svg[width="300",role="middle"]
 .Considerations
 |===
 | `null` is returned if the `list` is `null` or if the `predicate` evaluates to `null` for at least one element and does not evaluate to false for any other element.
+| `any()` returns `false` if `list` is empty because there are no elements to satisfy the `predicate`.
 |===
 
 .+any()+
@@ -135,6 +154,24 @@ The query returns the `Person` nodes with the `nationality` property value `Amer
 
 |===
 
+
+.`any()` on an empty `LIST`
+[source, cypher]
+----
+WITH [] as emptyList
+RETURN any(i IN emptyList WHERE true) as anyTrue, any(i IN emptyList WHERE false) as anyFalse
+----
+
+.Result
+[role="queryresult",options="header,footer",cols="2*<m"]
+|===
+| anyTrue | anyFalse
+
+| FALSE  | FALSE
+
+2+d|Rows: 1
+|===
+
 ======
 
 
@@ -312,6 +349,7 @@ xref:syntax/operators.adoc#cypher-comparison[`IS NULL` or `IS NOT NULL`] should
 .Considerations
 |===
 | `null` is returned if the `list` is `null`, or if the `predicate` evaluates to `null` for at least one element and does not evaluate to `true` for any other element.
+| `none()` returns `true` if `list` is empty because there are no elements to violate the `predicate`.
 |===
 
 .+none()+
@@ -345,6 +383,23 @@ image::predicate_function_example.svg[width="300",role="middle"]
 
 |===
 
+.`none()` on an empty `LIST`
+[source, cypher]
+----
+WITH [] as emptyList
+RETURN none(i IN emptyList WHERE true) as noneTrue, none(i IN emptyList WHERE false) as noneFalse
+----
+
+.Result
+[role="queryresult",options="header,footer",cols="2*<m"]
+|===
+| noneTrue | noneFalse
+
+| TRUE  | TRUE
+
+2+d|Rows: 1
+|===
+
 ======
 
 
@@ -365,6 +420,7 @@ image::predicate_function_example.svg[width="300",role="middle"]
 .Considerations
 |===
 | `null` is returned if the `list` is `null`, or if the `predicate` evaluates to `null` for at least one element and does not evaluate to `true` for any other element.
+| `single()` returns `false` if `list` is empty because there is not exactly one element satisfying the `predicate`.
 |===
 
 .+single()+
@@ -394,4 +450,21 @@ In every returned path there is exactly one node which has the `nationality` pro
 
 |===
 
+.`single()` on an empty `LIST`
+[source, cypher]
+----
+WITH [] as emptyList
+RETURN single(i IN emptyList WHERE true) as singleTrue, single(i IN emptyList WHERE false) as singleFalse
+----
+
+.Result
+[role="queryresult",options="header,footer",cols="2*<m"]
+|===
+| singleTrue | singleFalse
+
+| FALSE  | FALSE
+
+2+d|Rows: 1
+|===
+
 ======