Add documentation for using sets as arguments.

docs/datamodel/functions.rst

@@ -34,6 +34,48 @@ This function accepts a :eql:type:`str` as an argument and produces a
 
 .. _ref_datamodel_functions_modifying:
 
+Sets as arguments
+^^^^^^^^^^^^^^^^^
+
+Calling a user-defined function on a set will always apply it as
+:ref:`*element-wise* <_ref_reference_cardinality_functions_operators>`.
+
+.. code-block:: sdl
+
+  function magnitude(x: float64) -> float64
+    using (
+      math::sqrt(sum(x * x))
+    );
+
+.. code-block:: edgeql-repl
+
+    db> select magnitude({3, 4});
+    {3, 4}
+
+In order to pass in multiple arguments at once, arguments should be packed into
+arrays:
+
+.. code-block:: sdl
+
+  function magnitude(xs: array<float64>) -> float64
+    using (
+      with x := array_unpack(xs)
+      select math::sqrt(sum(x * x))
+    );
+
+.. code-block:: edgeql-repl
+
+    db> select magnitude([3, 4]);
+    {5}
+
+Multiple packed arrays can be passed into such a function, which will then be
+applied element-wise.
+
+.. code-block:: edgeql-repl
+
+    db> select magnitude({[3, 4], [5, 12]});
+    {5, 13}
+
 Modifying Functions
 ^^^^^^^^^^^^^^^^^^^
 
@@ -93,6 +135,18 @@ then the following queries are valid:
     db> select add_user('May', <datetime>'2024-12-11T12:00:00-07:00') {name, joined_at};
     {default::User {name: 'May', joined_at: <datetime>'2024-12-11T12:00:00Z'}}
 
+In order to insert or update a multi parameter, the desired arguments should be
+aggregated into an array as described above:
+
+.. code-block:: sdl
+
+  function add_user(name: str, nicknames: array<str>) -> User
+    using (
+      insert User {
+        name := name,
+        nicknames := array_unpack(nicknames),
+      }
+    );
 
 .. list-table::
   :class: seealso

docs/reference/edgeql/cardinality.rst

@@ -22,6 +22,8 @@ instance, when assigning to a ``required multi`` link, the value being
 assigned in question *must* have a cardinality of ``One`` or ``AtLeastOne``
 (as empty sets are not permitted).
 
+.. _ref_reference_cardinality_functions_operators:
+
 Functions and operators
 -----------------------
 

docs/reference/sdl/functions.rst

@@ -101,6 +101,8 @@ This declaration defines a new constraint with the following options:
     argument as a *whole set*, as opposed to being called on the input
     product element-by-element.
 
+    User defined functions can not use ``set of`` arguments.
+
     The ``optional`` qualifier indicates that the function will be called
     if the argument is an empty set.  The default behavior is to return
     an empty set if the argument is not marked as ``optional``.