with FUNDAMENTALS; use FUNDAMENTALS;
with FUNCT;        use FUNCT;

package environment_pkg is

type activation;
type activation_ptr is access activation;

type environment;
type environment_ptr is access environment;

--------------------------- type ACTIVATION -----------------------------
-- for activation records.  A name field is provided solely
--   for debugging purposes.  Control links and activation links are
--   provided.  Activation records must also contain the values bound to
--   both the parameters and function names used by the function being
--   activated.
-- No functions are defined explicitly for activation records, but
--   several functions defined on environments (see below) have the
--   effect of processing activation records.

type activation is record
  name:symbol_type_ptr;             -- just for debugging
  control_ptr:activation_ptr;
  access_ptr:activation_ptr;
  actuals:list_of_offsets_ptr;
  functs:list_of_functions_ptr;
end record;


--------------------------- type ENVIRONMENT  -----------------------------
-- An environment object is just a linked list of activation records.
--   Since these records are linked both by control links and by
--   activation links, the links are stored in the activation records,
--   so that the only field of an environment object is a
--   pointer to the first activation record.
-- Nonetheless, many useful functions take an ENVIRONMENT argument,
--   e.g., the functions that PUSH and POP activation records to or from
--   the environment.  The PUSH function takes an integer argument
--   describing how far back to link the access pointer.  The POP
--   function returns nothing since the value popped is not needed.
-- Another example is the function that runs a compiled "program".  Actually
--   there are two such functions -- one that handles a top level function
--   (taking only a pointer to a function object as parameter) and one that
--   handles all other functions (also taking a representation of the call).
-- Other such functions look up the bodies of functions in the
--   environment, look up the values of variables in the
--   environment, and bind formals to actuals in the environment.

type environment is record
  first:activation_ptr;
end record;

procedure push(e:environment_ptr; a:activation_ptr; i:integer);
procedure pop(e:environment_ptr);
procedure run(e:environment_ptr; f:function_ptr);
procedure run(e:environment_ptr; call:list_of_offsets_ptr; f:function_ptr);
function get_function(e:environment_ptr; o:offset_ptr) return function_ptr;
function eval(e:environment_ptr; o:offset_ptr) return offset_ptr;
procedure bind(e:environment_ptr; call:list_of_offsets_ptr;
                                  actuals:list_of_offsets_ptr);


end environment_pkg;