Document the Void type

nstack · May 10, 2017 · 576a64b · 576a64b
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diff --git a/reference/supported_types.rst b/reference/supported_types.rst
@@ -28,4 +28,7 @@ More complex types can be built out of primitive ones:
 * Arrays: ``[type1]``
 * `Sums <https://en.wikipedia.org/wiki/Algebraic_data_type>`_: ``Name1 type1a ... | Name2 type2a ... | ...``
 
+``Void`` is a special type that is used to define custom sources and sinks,
+see :ref:`supported-integrations`.
+
 A user can define their own type in the :ref:`workflow_language`.
diff --git a/reference/workflow_language.rst b/reference/workflow_language.rst
@@ -176,8 +176,9 @@ The syntax is defined in EBNF (ISO/IEC 14977) in terms of tokens.
   import = 'import', module name, 'as', module alias;
   type = 'type', name, '=', ( type expression | sum type );
   declaration = 'fun', name, ':', type expression,
-                            '->', type expression;
+                            '->', top-level type expression;
   definition = 'def', name, '=', expression;
+  top-level type expression = type expression | 'Void';
   type expression = type expression1
                   | 'optional', type expression 1
                   ;