cursor
This class implements the ‘cursor’ and the ‘repeat’ (loop) expressions.
The cursor expression is a kind of enhanced ‘sequence’. Like a sequence
it will execute its child expression one by one, sequentially. Unlike a
sequence though, it will obey ‘commands’.
cursor do
author
reviewer
rewind :if => '${f:not_ok}'
publisher
end
In this simplistic example, the process will flow from author to reviewer
and back until the reviewer sets the workitem field ‘not_ok’ to something
else than the value ‘true’.
There are two ways to pass commands to a cursor either directly from
the process definition with a cursor command expression, either via
the workitem ‘command’ [special] field.
cursor commands
The commands that a cursor understands are listed here. The most powerful
ones are ‘rewind’ and ‘jump’.
rewind
Rewinds the cursor up to its first child expression.
cursor do
author
reviewer
rewind :if => '${f:not_ok}'
publisher
end
reset
Whereas ‘rewind’ places the cursor back to the initial step with the current
workitem, ‘reset’ will rewind it and start again but with the workitem
as it was when it reached the cursor/repeat.
stop, over & break
Exits the cursor.
cursor do
author
reviewer
rewind :if => '${f:review} == fix'
stop :if => '${f:review} == abort'
publisher
end
‘_break’ or ‘over’ can be used instead of ‘stop’.
skip & back
Those two commands jump forth and back respectively. By default, they
skip 1 child, but they accept a numeric parameter holding the number
of children to skip.
cursor do
author
reviewer
rewind :if => '${f:review} == fix'
skip 2 :if => '${f:review} == publish'
reviewer2
rewind :if => '${f:review} == fix'
publisher
end
jump
Jump is probably the most powerful of the cursor commands. It allows to
jump to a specified expression that is a direct child of the cursor.
cursor do
author
reviewer
jump :to => 'author', :if => '${f:review} == fix'
jump :to => 'publisher', :if => '${f:review} == publish'
reviewer2
jump :to => 'author', :if => '${f:review} == fix'
publisher
end
Note that the :to accepts the name of an expression or the value of
its :ref attribute or the value of its :tag attribute.
cursor do
participant :ref => 'author'
participant :ref => 'reviewer'
jump :to => 'author', :if => '${f:review} == fix'
participant :ref => 'publisher'
end
cursor command with :ref
It’s OK to tag a cursor/repeat/loop with the :tag attribute and then
point a command to it via :ref :
concurrence do
cursor :tag => 'main' do
author
editor
publisher
end
# meanwhile ...
sequence do
sponsor
rewind :ref => 'main', :if => '${f:stop}'
end
end
This :ref technique may also be used with nested cursor/loop/iterator
constructs :
cursor :tag => 'main' do
cursor do
author
editor
rewind :if => '${f:not_ok}'
_break :ref => 'main', :if => '${f:abort_everything}'
end
head_of_edition
rewind :if => '${f:not_ok}'
publisher
end
this example features two nested cursors. There is a “_break” in the inner
cursor, but it will break the main ‘cursor’ (and thus break the whole
review process).
cursor command in the workitem
The command expressions are merely setting the workitem field ‘command’
with an array value [ {command}, {arg} ].
For example,
jump :to => 'author'
# is equivalent to
set 'field:__command__' => 'author'
It is entirely OK to have a participant implementation that sets command
by itself.
class Reviewer
include Ruote::LocalParticipant
def consume(workitem)
# somehow review the book
if review == 'bad'
#workitem.fields['__command__'] = [ 'rewind' ] # old style
workitem.command = 'rewind' # new style
else
# let it go
end
reply_to_engine(workitem)
end
def cancel(fei, flavour)
# cancel if review is still going on...
end
end
This example uses the Ruote::Workitem#command= method which can be fed
strings like ‘rewind’, ‘skip 2’, ‘jump to author’ or the equivalent arrays
[ ‘rewind’ ], [ ‘skip’, 2 ], [ ‘jump’, ‘author’ ].
:break_if / :rewind_if
As an attribute of the cursor/repeat expression, you can set a :break_if.
It tells the cursor (loop) if it has to break.
cursor :break_if => '${f:completed}' do
participant 'alpha'
participant 'bravo'
participant 'charly'
end
If alpha or bravo replies and the field ‘completed’ is set to true, this
cursor will break.
:break_unless is accepted. :over_if and :over_unless are synonyms for
:break_if and :break_unless respectively.
:rewind_if / :rewind_unless behave the same, but the cursor/loop, instead
of breaking, is put back in its first step.
repeat (loop)
A ‘cursor’ expression exits implicitely as soon as its last child replies
to it.
a ‘repeat’ expression will apply (again) the first child after the last
child replied. A ‘break’ cursor command might be necessary to exit the loop
(or a cancel_process, but that exits the whole process instance).
sequence do
repeat do
author
reviewer
_break :if => '${f:review} == ok'
end
publisher
end