------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--                                S C A N S                                 --
--                                                                          --
--                                 S p e c                                  --
--                                                                          --
--                            $Revision: 1.35 $
--                                                                          --
--          Copyright (C) 1992-2001 Free Software Foundation, Inc.          --
--                                                                          --
-- GNAT is free software;  you can  redistribute it  and/or modify it under --
-- terms of the  GNU General Public License as published  by the Free Soft- --
-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
-- for  more details.  You should have  received  a copy of the GNU General --
-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
-- MA 02111-1307, USA.                                                      --
--                                                                          --
-- As a special exception,  if other files  instantiate  generics from this --
-- unit, or you link  this unit with other files  to produce an executable, --
-- this  unit  does not  by itself cause  the resulting  executable  to  be --
-- covered  by the  GNU  General  Public  License.  This exception does not --
-- however invalidate  any other reasons why  the executable file  might be --
-- covered by the  GNU Public License.                                      --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
--                                                                          --
------------------------------------------------------------------------------

with Types; use Types;

package Scans is

--  The scanner maintains a current state in the global variables defined
--  in this package. The call to the Scan routine advances this state to
--  the next token. The state is initialized by the call to one of the
--  initialization routines in Sinput.

   --  The following type is used to identify token types returned by Scan.
   --  The class column in this table indicates the token classes which
   --  apply to the token, as defined by subsquent subtype declarations.

   --  Note: the coding in SCN depends on the fact that the first entry in
   --  this type declaration is *not* for a reserved word. For details on
   --  why there is this requirement, see Scn.Initialize_Scanner.

   type Token_Type is (

      --  Token name          Token type   Class(es)

      Tok_Integer_Literal, -- numeric lit  Literal, Lit_Or_Name

      Tok_Real_Literal,    -- numeric lit  Literal, Lit_Or_Name

      Tok_String_Literal,  -- string lit   Literal. Lit_Or_Name

      Tok_Char_Literal,    -- char lit     Name, Literal. Lit_Or_Name

      Tok_Operator_Symbol, -- op symbol    Name, Literal, Lit_Or_Name, Desig

      Tok_Identifier,      -- identifer    Name, Lit_Or_Name, Desig

      Tok_Double_Asterisk, -- **

      Tok_Ampersand,       -- &            Binary_Addop
      Tok_Minus,           -- -            Binary_Addop, Unary_Addop
      Tok_Plus,            -- +            Binary_Addop, Unary_Addop

      Tok_Asterisk,        -- *            Mulop
      Tok_Mod,             -- MOD          Mulop
      Tok_Rem,             -- REM          Mulop
      Tok_Slash,           -- /            Mulop

      Tok_New,             -- NEW

      Tok_Abs,             -- ABS
      Tok_Others,          -- OTHERS
      Tok_Null,            -- NULL

      Tok_Dot,             -- .            Namext
      Tok_Apostrophe,      -- '            Namext

      Tok_Left_Paren,      -- (            Namext, Consk

      Tok_Delta,           -- DELTA        Atkwd, Sterm, Consk
      Tok_Digits,          -- DIGITS       Atkwd, Sterm, Consk
      Tok_Range,           -- RANGE        Atkwd, Sterm, Consk

      Tok_Right_Paren,     -- )            Sterm
      Tok_Comma,           -- ,            Sterm

      Tok_And,             -- AND          Logop, Sterm
      Tok_Or,              -- OR           Logop, Sterm
      Tok_Xor,             -- XOR          Logop, Sterm

      Tok_Less,            -- <            Relop, Sterm
      Tok_Equal,           -- =            Relop, Sterm
      Tok_Greater,         -- >            Relop, Sterm
      Tok_Not_Equal,       -- /=           Relop, Sterm
      Tok_Greater_Equal,   -- >=           Relop, Sterm
      Tok_Less_Equal,      -- <=           Relop, Sterm

      Tok_In,              -- IN           Relop, Sterm
      Tok_Not,             -- NOT          Relop, Sterm

      Tok_Box,             -- <>           Relop, Eterm, Sterm
      Tok_Colon_Equal,     -- :=           Eterm, Sterm
      Tok_Colon,           -- :            Eterm, Sterm
      Tok_Greater_Greater, -- >>           Eterm, Sterm

      Tok_Abstract,        -- ABSTRACT     Eterm, Sterm
      Tok_Access,          -- ACCESS       Eterm, Sterm
      Tok_Aliased,         -- ALIASED      Eterm, Sterm
      Tok_All,             -- ALL          Eterm, Sterm
      Tok_Array,           -- ARRAY        Eterm, Sterm
      Tok_At,              -- AT           Eterm, Sterm
      Tok_Body,            -- BODY         Eterm, Sterm
      Tok_Constant,        -- CONSTANT     Eterm, Sterm
      Tok_Do,              -- DO           Eterm, Sterm
      Tok_Is,              -- IS           Eterm, Sterm
      Tok_Limited,         -- LIMITED      Eterm, Sterm
      Tok_Of,              -- OF           Eterm, Sterm
      Tok_Out,             -- OUT          Eterm, Sterm
      Tok_Record,          -- RECORD       Eterm, Sterm
      Tok_Renames,         -- RENAMES      Eterm, Sterm
      Tok_Reverse,         -- REVERSE      Eterm, Sterm
      Tok_Tagged,          -- TAGGED       Eterm, Sterm
      Tok_Then,            -- THEN         Eterm, Sterm

      Tok_Less_Less,       -- <<           Eterm, Sterm, After_SM

      Tok_Abort,           -- ABORT        Eterm, Sterm, After_SM
      Tok_Accept,          -- ACCEPT       Eterm, Sterm, After_SM
      Tok_Case,            -- CASE         Eterm, Sterm, After_SM
      Tok_Delay,           -- DELAY        Eterm, Sterm, After_SM
      Tok_Else,            -- ELSE         Eterm, Sterm, After_SM
      Tok_Elsif,           -- ELSIF        Eterm, Sterm, After_SM
      Tok_End,             -- END          Eterm, Sterm, After_SM
      Tok_Exception,       -- EXCEPTION    Eterm, Sterm, After_SM
      Tok_Exit,            -- EXIT         Eterm, Sterm, After_SM
      Tok_Goto,            -- GOTO         Eterm, Sterm, After_SM
      Tok_If,              -- IF           Eterm, Sterm, After_SM
      Tok_Pragma,          -- PRAGMA       Eterm, Sterm, After_SM
      Tok_Raise,           -- RAISE        Eterm, Sterm, After_SM
      Tok_Requeue,         -- REQUEUE      Eterm, Sterm, After_SM
      Tok_Return,          -- RETURN       Eterm, Sterm, After_SM
      Tok_Select,          -- SELECT       Eterm, Sterm, After_SM
      Tok_Terminate,       -- TERMINATE    Eterm, Sterm, After_SM
      Tok_Until,           -- UNTIL        Eterm, Sterm, After_SM
      Tok_When,            -- WHEN         Eterm, Sterm, After_SM

      Tok_Begin,           -- BEGIN        Eterm, Sterm, After_SM, Labeled_Stmt
      Tok_Declare,         -- DECLARE      Eterm, Sterm, After_SM, Labeled_Stmt
      Tok_For,             -- FOR          Eterm, Sterm, After_SM, Labeled_Stmt
      Tok_Loop,            -- LOOP         Eterm, Sterm, After_SM, Labeled_Stmt
      Tok_While,           -- WHILE        Eterm, Sterm, After_SM, Labeled_Stmt

      Tok_Entry,           -- ENTRY        Eterm, Sterm, Declk, Deckn, After_SM
      Tok_Protected,       -- PROTECTED    Eterm, Sterm, Declk, Deckn, After_SM
      Tok_Task,            -- TASK         Eterm, Sterm, Declk, Deckn, After_SM
      Tok_Type,            -- TYPE         Eterm, Sterm, Declk, Deckn, After_SM
      Tok_Subtype,         -- SUBTYPE      Eterm, Sterm, Declk, Deckn, After_SM
      Tok_Use,             -- USE          Eterm, Sterm, Declk, Deckn, After_SM

      Tok_Function,        -- FUNCTION     Eterm, Sterm, Cunit, Declk, After_SM
      Tok_Generic,         -- GENERIC      Eterm, Sterm, Cunit, Declk, After_SM
      Tok_Package,         -- PACKAGE      Eterm, Sterm, Cunit, Declk, After_SM
      Tok_Procedure,       -- PROCEDURE    Eterm, Sterm, Cunit, Declk, After_SM

      Tok_Private,         -- PRIVATE      Eterm, Sterm, Cunit, After_SM
      Tok_With,            -- WITH         Eterm, Sterm, Cunit, After_SM
      Tok_Separate,        -- SEPARATE     Eterm, Sterm, Cunit, After_SM

      Tok_EOF,             -- End of file  Eterm, Sterm, Cterm, After_SM

      Tok_Semicolon,       -- ;            Eterm, Sterm, Cterm

      Tok_Arrow,           -- =>           Sterm, Cterm, Chtok

      Tok_Vertical_Bar,    -- |            Cterm, Sterm, Chtok

      Tok_Dot_Dot,         -- ..           Sterm, Chtok

      --  The following three entries are used only when scanning
      --  project files.

      Tok_Project,
      Tok_Extends,
      Tok_External,

      No_Token);
      --  No_Token is used for initializing Token values to indicate that
      --  no value has been set yet.

   --  Note: in the RM, operator symbol is a special case of string literal.
   --  We distinguish at the lexical level in this compiler, since there are
   --  many syntactic situations in which only an operator symbol is allowed.

   --  The following subtype declarations group the token types into classes.
   --  These are used for class tests in the parser.

      subtype Token_Class_Numeric_Literal is
        Token_Type range Tok_Integer_Literal .. Tok_Real_Literal;
      --  Numeric literal

      subtype Token_Class_Literal is
        Token_Type range Tok_Integer_Literal .. Tok_Operator_Symbol;
      --  Literal

      subtype Token_Class_Lit_Or_Name is
        Token_Type range Tok_Integer_Literal .. Tok_Identifier;

      subtype Token_Class_Binary_Addop is
        Token_Type range Tok_Ampersand .. Tok_Plus;
      --  Binary adding operator (& + -)

      subtype Token_Class_Unary_Addop is
        Token_Type range Tok_Minus .. Tok_Plus;
      --  Unary adding operator (+ -)

      subtype Token_Class_Mulop is
        Token_Type range Tok_Asterisk .. Tok_Slash;
      --  Multiplying operator

      subtype Token_Class_Logop is
        Token_Type range Tok_And .. Tok_Xor;
      --  Logical operator (and, or, xor)

      subtype Token_Class_Relop is
        Token_Type range Tok_Less .. Tok_Box;
      --  Relational operator (= /= < <= > >= not, in plus <> to catch misuse
      --  of Pascal style not equal operator).

      subtype Token_Class_Name is
        Token_Type range Tok_Char_Literal .. Tok_Identifier;
      --  First token of name (4.1),
      --    (identifier, char literal, operator symbol)

      subtype Token_Class_Desig is
        Token_Type range Tok_Operator_Symbol .. Tok_Identifier;
      --  Token which can be a Designator (identifier, operator symbol)

      subtype Token_Class_Namext is
        Token_Type range Tok_Dot .. Tok_Left_Paren;
      --  Name extension tokens. These are tokens which can appear immediately
      --  after a name to extend it recursively (period, quote, left paren)

      subtype Token_Class_Consk is
        Token_Type range Tok_Left_Paren .. Tok_Range;
      --  Keywords which can start constraint
      --    (left paren, delta, digits, range)

      subtype Token_Class_Eterm is
        Token_Type range Tok_Colon_Equal .. Tok_Semicolon;
      --  Expression terminators. These tokens can never appear within a simple
      --  expression. This is used for error recovery purposes (if we encounter
      --  an error in an expression, we simply scan to the next Eterm token).

      subtype Token_Class_Sterm is
        Token_Type range Tok_Delta .. Tok_Dot_Dot;
      --  Simple_Expression terminators. A Simple_Expression must be followed
      --  by a token in this class, or an error message is issued complaining
      --  about a missing binary operator.

      subtype Token_Class_Atkwd is
        Token_Type range Tok_Delta .. Tok_Range;
      --  Attribute keywords. This class includes keywords which can be used
      --  as an Attribute_Designator, namely DELTA, DIGITS and RANGE

      subtype Token_Class_Cterm is
        Token_Type range Tok_EOF .. Tok_Vertical_Bar;
      --  Choice terminators. These tokens terminate a choice. This is used for
      --  error recovery purposes (if we encounter an error in a Choice, we
      --  simply scan to the next Cterm token).

      subtype Token_Class_Chtok is
        Token_Type range Tok_Arrow .. Tok_Dot_Dot;
      --  Choice tokens. These tokens signal a choice when used in an Aggregate

      subtype Token_Class_Cunit is
        Token_Type range Tok_Function .. Tok_Separate;
      --  Tokens which can begin a compilation unit

      subtype Token_Class_Declk is
        Token_Type range Tok_Entry .. Tok_Procedure;
      --  Keywords which start a declaration

      subtype Token_Class_Deckn is
        Token_Type range Tok_Entry .. Tok_Use;
      --  Keywords which start a declaration but can't start a compilation unit

      subtype Token_Class_After_SM is
        Token_Type range Tok_Less_Less .. Tok_EOF;
      --  Tokens which always, or almost always, appear after a semicolon. Used
      --  in the Resync_Past_Semicolon routine to avoid gobbling up stuff when
      --  a semicolon is missing. Of significance only for error recovery.

      subtype Token_Class_Labeled_Stmt is
        Token_Type range Tok_Begin .. Tok_While;
      --  Tokens which start labeled statements

      type Token_Flag_Array is array (Token_Type) of Boolean;
      Is_Reserved_Keyword : constant Token_Flag_Array := Token_Flag_Array'(
         Tok_Mod      .. Tok_Rem      => True,
         Tok_New      .. Tok_Null     => True,
         Tok_Delta    .. Tok_Range    => True,
         Tok_And      .. Tok_Xor      => True,
         Tok_In       .. Tok_Not      => True,
         Tok_Abstract .. Tok_Then     => True,
         Tok_Abort    .. Tok_Separate => True,
         others                       => False);
      --  Flag array used to test for reserved word

   --------------------------
   -- Scan State Variables --
   --------------------------

   --  Note: these variables can only be referenced during the parsing of a
   --  file. Reference to any of them from Sem or the expander is wrong.

   Scan_Ptr : Source_Ptr;
   --  Current scan pointer location. After a call to Scan, this points
   --  just past the end of the token just scanned.

   Token : Token_Type;
   --  Type of current token

   Token_Ptr : Source_Ptr;
   --  Pointer to first character of current token

   Current_Line_Start : Source_Ptr;
   --  Pointer to first character of line containing current token

   Start_Column : Column_Number;
   --  Starting column number (zero origin) of the first non-blank character
   --  on the line containing the current token. This is used for error
   --  recovery circuits which depend on looking at the column line up.

   Checksum : Word;
   --  Used to accumulate a CRC representing the tokens in the source
   --  file being compiled. This CRC includes only program tokens, and
   --  excludes comments.

   First_Non_Blank_Location : Source_Ptr;
   --  Location of first non-blank character on the line containing the
   --  current token (i.e. the location of the character whose column number
   --  is stored in Start_Column).

   Token_Node : Node_Id := Empty;
   --  Node table Id for the current token. This is set only if the current
   --  token is one for which the scanner constructs a node (i.e. it is an
   --  identifier, operator symbol, or literal. For other token types,
   --  Token_Node is undefined.

   Token_Name : Name_Id := No_Name;
   --  For identifiers, this is set to the Name_Id of the identifier scanned.
   --  For all other tokens, Token_Name is set to Error_Name. Note that it
   --  would be possible for the caller to extract this information from
   --  Token_Node. We set Token_Name separately for two reasons. First it
   --  allows a quicker test for a specific identifier. Second, it allows
   --  a version of the parser to be built that does not build tree nodes,
   --  usable as a syntax checker.

   Prev_Token : Token_Type := No_Token;
   --  Type of previous token

   Prev_Token_Ptr : Source_Ptr;
   --  Pointer to first character of previous token

   Version_To_Be_Found : Boolean;
   --  This flag is True if the scanner is still looking for an RCS version
   --  number in a comment. Normally it is initialized to False so that this
   --  circuit is not activated. If the -dv switch is set, then this flag is
   --  initialized to True, and then reset when the version number is found.
   --  We do things this way to minimize the impact on comment scanning.

   --------------------------------------------------------
   -- Procedures for Saving and Restoring the Scan State --
   --------------------------------------------------------

   --  The following procedures can be used to save and restore the entire
   --  scan state. They are used in cases where it is necessary to backup
   --  the scan during the parse.

   type Saved_Scan_State is private;
   --  Used for saving and restoring the scan state

   procedure Save_Scan_State (Saved_State : out Saved_Scan_State);
   pragma Inline (Save_Scan_State);
   --  Saves the current scan state for possible later restoration. Note that
   --  there is no harm in saving the state and then never restoring it.

   procedure Restore_Scan_State (Saved_State : in Saved_Scan_State);
   pragma Inline (Restore_Scan_State);
   --  Restores a scan state saved by a call to Save_Scan_State.
   --  The saved scan state must refer to the current source file.

private
   type Saved_Scan_State is record
      Save_Scan_Ptr                 : Source_Ptr;
      Save_Token                    : Token_Type;
      Save_Token_Ptr                : Source_Ptr;
      Save_Current_Line_Start       : Source_Ptr;
      Save_Start_Column             : Column_Number;
      Save_Checksum                 : Word;
      Save_First_Non_Blank_Location : Source_Ptr;
      Save_Token_Node               : Node_Id;
      Save_Token_Name               : Name_Id;
      Save_Prev_Token               : Token_Type;
      Save_Prev_Token_Ptr           : Source_Ptr;
   end record;

end Scans;
