# Copyright 2006 by Sean Luke and George Mason University
# Licensed under the Academic Free License version 3.0
# See the file "LICENSE" for more information

###### example params file, goes in ec/app/regression
parent.0 = ./noerc.params

# To require that the root of a tree be a given node, you
# simply need to set up the typing so that that node is
# the only node which is compatable with the tree's return
# type.  The way to do this is to make not one but two
# atomic types (in the example below, nil and root).  nil
# is the default type used by our GP nodes.  root will be
# the return type of the tree.  Then we create a set type
# which is compatable with both of them called nil-and-root,
# and set it up so the return type of our desired node
# (in this case, 'div'), returns nil-and-root.  Thus 'div'
# is legal to hang as root (and is the only such node), AND
# 'div' is still perfectly compatable as a child of other
# nodes as before.

# The gotcha: many GP node builders require that for every
# reachable type used by nodes in the function set there
# must exist at least one terminal (and ideally one nonterminal)
# in the function set which returns that type.  This is
# because many GP node builder algorithms insist on being
# able to emit a terminal whenever they so desire, regardless
# of what the current type situation is where the terminal
# has to be hung.  The notable exception to this is Uniform.

# Ordinarily this would be a problem for us as we use
# Ramped Half-and-Half as our builder, and it has this 
# requirement.  However since we are telling Ramped Half-and-Half
# to generate only trees of sizes 2 and up (NOT 1 and up), 
# it will never attempt to select a terminal for the root
# and this gotcha will not occur.  The issue would also come
# up if we use tree mutation as an operator rather than solely
# crossover.  But we're not doing that.

# Okay, here we go.

# Add an atomic type (root) and a set type
# (nil-and-root) which is compatible with both
# nil and root
gp.type.a.size = 2
gp.type.a.0.name = nil
gp.type.a.1.name = root
gp.type.s.size = 1
gp.type.s.0.name = nil-and-root
gp.type.s.0.size = 2
gp.type.s.0.member.0 = nil
gp.type.s.0.member.1 = root

# make a new contraints form for div which returns
# things of type nil-and-root.  This is compatable
# with all elements that accept nil (which will be
# all other functions), so div will still fit right in.
gp.nc.size = 8
gp.nc.7 = ec.gp.GPNodeConstraints
gp.nc.7.name = nc-returning-nil-and-root
gp.nc.7.returns = nil-and-root
gp.nc.7.size = 2
gp.nc.7.child.0 = nil
gp.nc.7.child.1 = nil

# redefine div to return things of type nil-and-root.
gp.fs.0.func.4.nc = nc-returning-nil-and-root

# define the tree so that it only accepts items that
# are compatible with root.  div will be the only
# such item.
gp.tc.0.returns = root

###### end example