I had a similar problem, you have to define extra types in the params files, for example I added gp.type.a.size = 3 gp.type.a.1.name = boolean gp.type.a.2.name = double Then you need to add new node constraints to use the new types gp.nc.7 = ec.gp.GPNodeConstraints gp.nc.7.name = logical2c gp.nc.7.returns = boolean gp.nc.7.size = 2 gp.nc.7.child.0 = boolean gp.nc.7.child.1 = boolean have a look at ec/app/regression/noerc2.params too for a full example using the set types too