mal/ada/step4_if_fn_do.adb

with Ada.Command_Line;
with Ada.Exceptions;
with Ada.Text_IO;
with Core;
with Envs;
with Eval_Callback;
with Printer;
with Reader;
with Smart_Pointers;
with Types;

procedure Step4_If_Fn_Do is

   use Types;

   function Eval (Param : Types.Mal_Handle; Env : Envs.Env_Handle)
   return Types.Mal_Handle;

   Debug : Boolean := False;


   function Read (Param : String) return Types.Mal_Handle is
   begin
      return Reader.Read_Str (Param);
   end Read;


   function Def_Fn (Args : List_Mal_Type; Env : Envs.Env_Handle)
		   return Mal_Handle is
      Name, Fn_Body, Res : Mal_Handle;
   begin
      Name := Car (Args);
      pragma Assert (Deref (Name).Sym_Type = Sym,
                     "Def_Fn: expected symbol as name");
      Fn_Body := Nth (Args, 1);
      Res := Eval (Fn_Body, Env);
      Envs.Set (Env, Deref_Sym (Name).Get_Sym, Res);
      return Res;
   end Def_Fn;


   function Let_Processing (Args : List_Mal_Type; Env : Envs.Env_Handle)
                          return Mal_Handle is
      Defs, Expr, Res : Mal_Handle;
      E : Envs.Env_Handle;
   begin
      E := Envs.New_Env (Env);
      Defs := Car (Args);
      Deref_List_Class (Defs).Add_Defs (E);
      Expr := Car (Deref_List (Cdr (Args)).all);
      Res := Eval (Expr, E);
      return Res;
   end Let_Processing;


   function Do_Processing (Do_List : List_Mal_Type; Env : Envs.Env_Handle)
                         return Mal_Handle is
      D : List_Mal_Type;
      Res : Mal_Handle := Smart_Pointers.Null_Smart_Pointer;
   begin
      if Debug then
         Ada.Text_IO.Put_Line ("Do-ing " & To_String (Do_List));
      end if;
      D := Do_List;
      while not Is_Null (D) loop
         Res := Eval (Car (D), Env);
         D := Deref_List (Cdr(D)).all;
      end loop;
      return Res;
   end Do_Processing;


   function Eval_As_Boolean (MH : Mal_Handle) return Boolean is
      Res : Boolean;
   begin
      case Deref (MH).Sym_Type is
         when Bool =>
            Res := Deref_Bool (MH).Get_Bool;
         when Nil =>
            return False;
--         when List =>
--            declare
--               L : List_Mal_Type;
--            begin
--               L := Deref_List (MH).all;
--               Res := not Is_Null (L);
--            end;
         when others => -- Everything else
            Res := True;
      end case;
      return Res;
   end Eval_As_Boolean;


   function Eval_Ast
     (Ast : Mal_Handle; Env : Envs.Env_Handle)
     return Mal_Handle is

      function Call_Eval (A : Mal_Handle) return Mal_Handle is
      begin
         return Eval (A, Env);
      end Call_Eval;

   begin

      case Deref (Ast).Sym_Type is

         when Sym =>

            declare
               Sym : Mal_String := Deref_Sym (Ast).Get_Sym;
            begin
               -- if keyword, return it. Otherwise look it up in the environment.
               if Sym(1) = ':' then
                  return Ast;
               else
                  return Envs.Get (Env, Sym);
               end if;
            exception
               when Envs.Not_Found =>
                  raise Envs.Not_Found with ("'" &  Sym & "' not found");
            end;

         when List =>

            return Map (Call_Eval'Unrestricted_Access, Deref_List_Class (Ast).all);

         when others => return Ast;

      end case;

   end Eval_Ast;


   function Eval (Param : Mal_Handle; Env : Envs.Env_Handle) return Mal_Handle is
      First_Param, Rest_Params : Mal_Handle;
      Rest_List, Param_List : List_Mal_Type;
   begin

      if Debug then
         Ada.Text_IO.Put_Line ("Evaling " & Deref (Param).To_String);
      end if;

      if Deref (Param).Sym_Type = List and then
	 Deref_List (Param).Get_List_Type = List_List then

         Param_List := Deref_List (Param).all;

         -- Deal with empty list..
         if Param_List.Length = 0 then
	    return Param;
         end if;

         First_Param := Car (Param_List);
         Rest_Params := Cdr (Param_List);
         Rest_List := Deref_List (Rest_Params).all;

         if Deref (First_Param).Sym_Type = Sym and then
            Deref_Sym (First_Param).Get_Sym = "def!" then

            return Def_Fn (Rest_List, Env);

         elsif Deref (First_Param).Sym_Type = Sym and then
               Deref_Sym (First_Param).Get_Sym = "let*" then

            return Let_Processing (Rest_List, Env);

         elsif Deref (First_Param).Sym_Type = Sym and then
               Deref_Sym (First_Param).Get_Sym = "do" then

            return Do_Processing (Rest_List, Env);

         elsif Deref (First_Param).Sym_Type = Sym and then
               Deref_Sym (First_Param).Get_Sym = "if" then

            declare
               Cond, True_Part, False_Part : Mal_Handle;
               Cond_Bool : Boolean;
               pragma Assert (Length (Rest_List) = 2 or Length (Rest_List) = 3,
                              "If_Processing: not 2 or 3 parameters");
               L : List_Mal_Type;
            begin

               Cond := Eval (Car (Rest_List), Env);

               Cond_Bool := Eval_As_Boolean (Cond);

               if Cond_Bool then
                  L := Deref_List (Cdr (Rest_List)).all;
                  return Eval (Car (L), Env);
               else
                  if Length (Rest_List) = 3 then
                     L := Deref_List (Cdr (Rest_List)).all;
                     L := Deref_List (Cdr (L)).all;
                     return Eval (Car (L), Env);
                  else
                     return New_Nil_Mal_Type;
                  end if;
               end if;

            end;

         elsif Deref (First_Param).Sym_Type = Sym and then
               Deref_Sym (First_Param).Get_Sym = "fn*" then

            return New_Lambda_Mal_Type
                     (Params => Car (Rest_List),
                      Expr => Nth (Rest_List, 1),
                      Env => Env);

         else

            -- The APPLY section.
            declare
               Evaled_H : Mal_Handle;
            begin
               Evaled_H := Eval_Ast (Param, Env);

               Param_List := Deref_List (Evaled_H).all;

               First_Param := Car (Param_List);
               Rest_Params := Cdr (Param_List);
               Rest_List := Deref_List (Rest_Params).all;

               if Deref (First_Param).Sym_Type = Func then
                  return Call_Func (Deref_Func (First_Param).all, Rest_Params);
               elsif Deref (First_Param).Sym_Type = Lambda then
                  return Apply (Deref_Lambda (First_Param).all, Rest_Params);
               else
                  raise Mal_Exception;
               end if;

            end;

         end if;

      else -- Not a List_List

         return Eval_Ast (Param, Env);

      end if;

   end Eval;


   function Print (Param : Types.Mal_Handle) return String is
   begin
      return Printer.Pr_Str (Param);
   end Print;


   function Rep (Param : String; Env : Envs.Env_Handle) return String is
      AST, Evaluated_AST : Types.Mal_Handle;
   begin

      AST := Read (Param);

      if Types.Is_Null (AST) then
         return "";
      else
         Evaluated_AST := Eval (AST, Env);
         return Print (Evaluated_AST);
      end if;

   end Rep;


   Repl_Env : Envs.Env_Handle;


   -- This op uses Repl_Env directly.


   procedure RE (Str : Mal_String) is
      Discarded : Mal_Handle;
   begin
      Discarded := Eval (Read (Str), Repl_Env);
   end RE;


   Cmd_Args : Natural;

begin

   -- Save a function pointer back to the Eval function.
   -- Can't use 'Access here because of Ada rules but 'Unrestricted_Access is OK
   -- as we know Eval will be in scope for the lifetime of the program.
   Eval_Callback.Eval := Eval'Unrestricted_Access;

   Cmd_Args := 0;
   while Ada.Command_Line.Argument_Count > Cmd_Args loop
     Cmd_Args := Cmd_Args + 1;
     if Ada.Command_Line.Argument (Cmd_Args) = "-d" then
        Debug := True;
     elsif Ada.Command_Line.Argument (Cmd_Args) = "-e" then
        Envs.Debug := True;
     end if;
   end loop;

   Repl_Env := Envs.New_Env;

   Core.Init (Repl_Env);

   RE ("(def! not (fn* (a) (if a false true)))");

   loop
      begin
         Ada.Text_IO.Put ("user> ");
         exit when Ada.Text_IO.End_Of_File;
         Ada.Text_IO.Put_Line (Rep (Ada.Text_IO.Get_Line, Repl_Env));
      exception
         when E : others =>
            Ada.Text_IO.Put_Line
              (Ada.Text_IO.Standard_Error,
               Ada.Exceptions.Exception_Information (E));
      end;
   end loop;
end Step4_If_Fn_Do;