doc-src/Codegen/Thy/examples/Codegen.hs

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;

module Codegen where {

import qualified Nat;

class Null a where {
  nulla :: a;
};

heada :: forall a. (Codegen.Null a) => [a] -> a;
heada (x : xs) = x;
heada [] = Codegen.nulla;

null_option :: forall a. Maybe a;
null_option = Nothing;

instance Codegen.Null (Maybe a) where {
  nulla = Codegen.null_option;
};

dummy :: Maybe Nat.Nat;
dummy = Codegen.heada [Just (Nat.Suc Nat.Zero_nat), Nothing];

}