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-rw-r--r--lib/stdlib/doc/src/gen_statem.xml82
1 files changed, 71 insertions, 11 deletions
diff --git a/lib/stdlib/doc/src/gen_statem.xml b/lib/stdlib/doc/src/gen_statem.xml
index 6fa2d86e0b..b20abbea5d 100644
--- a/lib/stdlib/doc/src/gen_statem.xml
+++ b/lib/stdlib/doc/src/gen_statem.xml
@@ -587,8 +587,8 @@ handle_event(_, _, State, Data) ->
<name name="state_enter"/>
<desc>
<p>
- If the state machine should use <em>state enter calls</em>
- is selected when starting the <c>gen_statem</c>
+ Whether the state machine should use <em>state enter calls</em>
+ or not is selected when starting the <c>gen_statem</c>
and after code change using the return value from
<seealso marker="#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso>.
</p>
@@ -606,7 +606,16 @@ handle_event(_, _, State, Data) ->
See
<seealso marker="#Module:StateName/3"><c>Module:StateName/3</c></seealso>
and
- <seealso marker="#Module:handle_event/4"><c>Module:handle_event/4</c></seealso>.
+ <seealso marker="#Module:handle_event/4"><c>Module:handle_event/4</c></seealso>.
+ Such a call can be repeated by returning a
+ <seealso marker="#type-state_callback_result">
+ <c>repeat_state</c>
+ </seealso>
+ or
+ <seealso marker="#type-state_callback_result">
+ <c>repeat_state_and_data</c>
+ </seealso>
+ tuple from the state callback.
</p>
<p>
If
@@ -625,7 +634,8 @@ handle_event(_, _, State, Data) ->
right before entering the initial state even though this
formally is not a state change.
In this case <c>OldState</c> will be the same as <c>State</c>,
- which can not happen for a subsequent state change.
+ which can not happen for a subsequent state change,
+ but will happen when repeating the state enter call.
</p>
</desc>
</datatype>
@@ -640,7 +650,15 @@ handle_event(_, _, State, Data) ->
<list type="ordered">
<item>
<p>
- If the state changes or is the initial state, and
+ If the state changes, is the initial state,
+ <seealso marker="#type-state_callback_result">
+ <c>repeat_state</c>
+ </seealso>
+ or
+ <seealso marker="#type-state_callback_result">
+ <c>repeat_state_and_data</c>
+ </seealso>
+ is used, and also
<seealso marker="#type-state_enter"><em>state enter calls</em></seealso>
are used, the <c>gen_statem</c> calls
the new state callback with arguments
@@ -1095,6 +1113,37 @@ handle_event(_, _, State, Data) ->
<c>{next_state,CurrentState,CurrentData,<anno>Actions</anno>}</c>.
</p>
</item>
+ <tag><c>repeat_state</c></tag>
+ <item>
+ <p>
+ The <c>gen_statem</c> keeps the current state, or
+ does a state transition to the current state if you like,
+ sets <c><anno>NewData</anno></c>,
+ and executes all <c><anno>Actions</anno></c>.
+ If the <c>gen_statem</c> runs with
+ <seealso marker="#type-state_enter"><em>state enter calls</em></seealso>,
+ the state enter call is repeated, see type
+ <seealso marker="#type-transition_option"><c>transition_option()</c></seealso>,
+ otherwise <c>repeat_state</c> is the same as
+ <c>keep_state</c>.
+ </p>
+ </item>
+ <tag><c>repeat_state_and_data</c></tag>
+ <item>
+ <p>
+ The <c>gen_statem</c> keeps the current state and data, or
+ does a state transition to the current state if you like,
+ and executes all <c><anno>Actions</anno></c>.
+ This is the same as
+ <c>{repeat_state,CurrentData,<anno>Actions</anno>}</c>.
+ If the <c>gen_statem</c> runs with
+ <seealso marker="#type-state_enter"><em>state enter calls</em></seealso>,
+ the state enter call is repeated, see type
+ <seealso marker="#type-transition_option"><c>transition_option()</c></seealso>,
+ otherwise <c>repeat_state_and_data</c> is the same as
+ <c>keep_state_and_data</c>.
+ </p>
+ </item>
<tag><c>stop</c></tag>
<item>
<p>
@@ -1870,22 +1919,33 @@ handle_event(_, _, State, Data) ->
<seealso marker="#type-enter_action">actions</seealso>
that may be returned:
<seealso marker="#type-postpone"><c>postpone()</c></seealso>
- and
+ is not allowed since a <em>state enter call</em> is not
+ an event so there is no event to postpone, and
<seealso marker="#type-action"><c>{next_event,_,_}</c></seealso>
- are not allowed.
+ is not allowed since using <em>state enter calls</em>
+ should not affect how events are consumed and produced.
You may also not change states from this call.
Should you return <c>{next_state,NextState, ...}</c>
with <c>NextState =/= State</c> the <c>gen_statem</c> crashes.
- You are advised to use <c>{keep_state,...}</c> or
- <c>keep_state_and_data</c>.
+ It is possible to use <c>{repeat_state, ...}</c>,
+ <c>{repeat_state_and_data,_}</c> or
+ <c>repeat_state_and_data</c> but all of them makes little
+ sense since you immediately will be called again with a new
+ <em>state enter call</em> making this just a weird way
+ of looping, and there are better ways to loop in Erlang.
+ You are advised to use <c>{keep_state,...}</c>,
+ <c>{keep_state_and_data,_}</c> or
+ <c>keep_state_and_data</c> since you can not change states
+ from a <em>state enter call</em> anyway.
</p>
<p>
Note the fact that you can use
<seealso marker="erts:erlang#throw/1"><c>throw</c></seealso>
to return the result, which can be useful.
For example to bail out with <c>throw(keep_state_and_data)</c>
- from deep within complex code that is in no position to
- return <c>{next_state,State,Data}</c>.
+ from deep within complex code that can not
+ return <c>{next_state,State,Data}</c> because
+ <c>State</c> or <c>Data</c> is no longer in scope.
</p>
</desc>
</func>