• w_leaf, w_share, w_copy, w_cycle and w_compound control the (compound) shape of the resulting term.
• w_atom, w_int, w_float, w_rational and w_string control what leaf node is generated after the group above decided to create a leaf.

Defaults:

#{
  depth:        5,          % maximum recursion depth
  depth_decay:  0.5,        % w_compound is scaled by this per level
  max_arity:    3,          % maximum compound arity
  functors:     [f,g,h,p,q],
  atoms:        [a,b,c],
  max_int:      100,        % random integer leaves in 0..max_int
  p_zero_arity: 0.1,	  % fraction on zero-arity compounds.
  w_leaf:       10,         % choice weights
  w_share:      30,
  w_copy:       15,
  w_cycle:      15,
  w_compound:   50,
  w_var:        10,         % leaf-type weights
  w_atom:       10,
  w_int:        10,
  w_float:      10,
  w_rational:   10,
  w_string:     10
}