doc-src/Codegen/Thy/examples/nat_binary.ML

more efficient Markup_Tree, based on branches sorted by quasi-order;
renamed markup_node.scala to markup_tree.scala and classes/objects accordingly;
Position.Range: produce actual Text.Range;
Symbol.Index.decode: convert 1-based Isabelle offsets here;
added static Command.range;
simplified Command.markup;
Document_Model.token_marker: flatten markup at most once;
tuned;

structure Nat = 
struct

datatype nat = Dig1 of nat | Dig0 of nat | One_nat | Zero_nat;

fun plus_nat (Dig1 m) (Dig1 n) = Dig0 (plus_nat (plus_nat m n) One_nat)
  | plus_nat (Dig1 m) (Dig0 n) = Dig1 (plus_nat m n)
  | plus_nat (Dig0 m) (Dig1 n) = Dig1 (plus_nat m n)
  | plus_nat (Dig0 m) (Dig0 n) = Dig0 (plus_nat m n)
  | plus_nat (Dig1 m) One_nat = Dig0 (plus_nat m One_nat)
  | plus_nat One_nat (Dig1 n) = Dig0 (plus_nat n One_nat)
  | plus_nat (Dig0 m) One_nat = Dig1 m
  | plus_nat One_nat (Dig0 n) = Dig1 n
  | plus_nat m Zero_nat = m
  | plus_nat Zero_nat n = n;

end; (*struct Nat*)