Automatic loops

This page discusses the possibility or getting rid of the awkward controlflow-style looping. We could allow modules to automatically loop if a module's port gets a list of values (or multiple connections).

typed lists?

• list shouldn't be a type like any other
  • allow connection List<T> -> T
  • allow connection T -> List<T> (make a one-element list, or actual list if the module loops)

• RR proposes: don't duplicate modules to loop, just make update() call compute() several times

• probably needs the dont-use-modules-as-data work -- modules that return themselves are going to break

• add logic in vistrails_module:Module:
  

if inputport T and input list<T>, call compute several times and build list of outputs

• coupling problem

  def test_module(a:T, b:T) -> (c:T, d:T):
  c = a*b
  d = a+b
  test_module([1, 2], [3, 4])

  • is it c = [3, 8], d = [4, 6]? (pairwise)
  • is it c = [3, 4, 6, 8], d = [4, 5, 5, 6]? (cartesian)
  • can probably be settable in module conf (and default to pairwise)

Implementation

The branch automatic-loops contains a working version using a ListOf module type.

References

How Taverna does it: http://dev.mygrid.org.uk/wiki/display/taverna/Loops