Ruote::Exp::ApplyExpression

The 'apply' expression is an advanced expression.

It takes as input an AST and applies it. The AST may be placed in a field or a variable or passed directly to the apply.

These apply examples :

apply :tree => [ 'echo', { 'nada' => nil }, [] ]

sequence do
  set :var => 'tree', :val => [ 'echo', { 'nada' => nil }, [] ]
  apply # looks by default in variable 'tree'
end

sequence do
  set :var => 't', :val => [ 'echo', { 'nada' => nil }, [] ]
  apply :tree_var => 't'
end

sequence do
  set :field => 't', :val => [ 'echo', { 'nada' => nil }, [] ]
  apply :tree_field => 't'
end

All are equivalent to

echo 'nada'

apply and subprocesses

There is an interesting way of using 'apply', it's close to the way of the Ruby "yield" expression.

pdef = Ruote.process_definition 'test' do
  sequence do
    handle do
      participant 'alpha'
    end
    handle do
      participant 'bravo'
    end
  end
  define 'handle' do
    sequence do
      participant 'prepare_data'
      apply
      participant 'rearrange_data'
    end
  end
end

With this process definition, the particpant alpha and bravo are handed a workitem in sequence, but each time, the data gets prepared and re-arranged.

'apply' simply picks the value of the tree to apply in the local variable 'tree'.

Passing variables to applied trees is possible :

pdef = Ruote.process_definition do
  handle do
    participant '${v:target}', :message => 'x'
  end
  define 'handle' do
    sequence do
      participant 'prepare_data'
      apply :v => 'alpha'
      apply :v => 'bravo'
      participant 'rearrange_data'
    end
  end
end

on_error

It's OK, to place an on_error on the apply

pdef = Ruote.process_definition do
  handle do
    sequence do
      echo 'in'
      nemo
    end
  end
  define 'handle' do
    apply :on_error => 'notify' # <==
    echo 'over.'
  end
  define 'notify' do
    echo 'error'
  end
end