gcc/ada/scans.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                                S C A N S                                 --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2023, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
  19 -- http://www.gnu.org/licenses for a complete copy of the license.          --
  20 --                                                                          --
  21 -- GNAT was originally developed  by the GNAT team at  New York University. --
  22 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  23 --                                                                          --
  24 ------------------------------------------------------------------------------
  25
  26 with Namet;  use Namet;
  27 with Types;  use Types;
  28 with Uintp;  use Uintp;
  29 with Urealp; use Urealp;
  30
  31 package Scans is
  32
  33 --  The scanner maintains a current state in the global variables defined
  34 --  in this package. The call to the Scan routine advances this state to
  35 --  the next token. The state is initialized by the call to one of the
  36 --  initialization routines in Sinput.
  37
  38    --  The following type is used to identify token types returned by Scan.
  39    --  The class column in this table indicates the token classes which
  40    --  apply to the token, as defined by subsequent subtype declarations.
  41
  42    type Token_Type is (
  43
  44       --  Token name          Token type   Class(es)
  45
  46       Tok_Integer_Literal, -- numeric lit  Literal, Lit_Or_Name
  47
  48       Tok_Real_Literal,    -- numeric lit  Literal, Lit_Or_Name
  49
  50       Tok_String_Literal,  -- string lit   Literal. Lit_Or_Name
  51
  52       Tok_Char_Literal,    -- char lit     Name, Literal. Lit_Or_Name
  53
  54       Tok_Operator_Symbol, -- op symbol    Name, Literal, Lit_Or_Name, Desig
  55
  56       Tok_Identifier,      -- identifier   Name, Lit_Or_Name, Desig
  57
  58       Tok_At_Sign,         -- @  AI12-0125-3 : target name
  59
  60       Tok_Double_Asterisk, -- **
  61
  62       Tok_Ampersand,       -- &            Binary_Addop
  63       Tok_Minus,           -- -            Binary_Addop, Unary_Addop
  64       Tok_Plus,            -- +            Binary_Addop, Unary_Addop
  65
  66       Tok_Asterisk,        -- *            Mulop
  67       Tok_Mod,             -- MOD          Mulop
  68       Tok_Rem,             -- REM          Mulop
  69       Tok_Slash,           -- /            Mulop
  70
  71       Tok_New,             -- NEW
  72
  73       Tok_Abs,             -- ABS
  74       Tok_Others,          -- OTHERS
  75       Tok_Null,            -- NULL
  76
  77       --  Note: Tok_Raise is in no categories now, it used to be Cterm, Eterm,
  78       --  After_SM, but now that Ada 2012 has added raise expressions, the
  79       --  raise token can appear anywhere. Note in particular that Tok_Raise
  80       --  being in Eterm stopped the parser from recognizing "return raise
  81       --  exception-name". This degrades error recovery slightly, and perhaps
  82       --  we could do better, but not worth the effort.
  83
  84       --  Ada 2022 introduces square brackets as delimiters for array and
  85       --  container aggregates.
  86
  87       --  The left delimiter token of interpolated strings, and tokens { and }
  88       --  of interpolated expressions are currently placed in no category since
  89       --  they don't fit well in the existing categories.
  90
  91       Tok_Left_Interpolated_String, -- f"
  92       Tok_Left_Curly_Bracket,       -- {
  93       Tok_Raise,                    -- RAISE
  94       Tok_Right_Curly_Bracket,      -- }
  95
  96       Tok_Dot,             -- .            Namext
  97       Tok_Apostrophe,      -- '            Namext
  98
  99       Tok_Left_Bracket,    -- [            Namext
 100       Tok_Left_Paren,      -- (            Namext, Consk
 101
 102       Tok_Delta,           -- DELTA        Atkwd, Sterm, Consk
 103       Tok_Digits,          -- DIGITS       Atkwd, Sterm, Consk
 104       Tok_Range,           -- RANGE        Atkwd, Sterm, Consk
 105
 106       Tok_Right_Paren,     -- )            Sterm
 107       Tok_Right_Bracket,   -- ]            Sterm
 108       Tok_Comma,           -- ,            Sterm
 109
 110       Tok_And,             -- AND          Logop, Sterm
 111       Tok_Or,              -- OR           Logop, Sterm
 112       Tok_Xor,             -- XOR          Logop, Sterm
 113
 114       Tok_Less,            -- <            Relop, Sterm
 115       Tok_Equal,           -- =            Relop, Sterm
 116       Tok_Greater,         -- >            Relop, Sterm
 117       Tok_Not_Equal,       -- /=           Relop, Sterm
 118       Tok_Greater_Equal,   -- >=           Relop, Sterm
 119       Tok_Less_Equal,      -- <=           Relop, Sterm
 120
 121       Tok_In,              -- IN           Relop, Sterm
 122       Tok_Not,             -- NOT          Relop, Sterm
 123
 124       Tok_Box,             -- <>           Relop, Eterm, Sterm
 125       Tok_Colon_Equal,     -- :=           Eterm, Sterm
 126       Tok_Colon,           -- :            Eterm, Sterm
 127       Tok_Greater_Greater, -- >>           Eterm, Sterm
 128
 129       Tok_Abstract,        -- ABSTRACT     Eterm, Sterm
 130       Tok_Access,          -- ACCESS       Eterm, Sterm
 131       Tok_Aliased,         -- ALIASED      Eterm, Sterm
 132       Tok_All,             -- ALL          Eterm, Sterm
 133       Tok_Array,           -- ARRAY        Eterm, Sterm
 134       Tok_At,              -- AT           Eterm, Sterm
 135       Tok_Body,            -- BODY         Eterm, Sterm
 136       Tok_Constant,        -- CONSTANT     Eterm, Sterm
 137       Tok_Do,              -- DO           Eterm, Sterm
 138       Tok_Is,              -- IS           Eterm, Sterm
 139       Tok_Interface,       -- INTERFACE    Eterm, Sterm
 140       Tok_Limited,         -- LIMITED      Eterm, Sterm
 141       Tok_Of,              -- OF           Eterm, Sterm
 142       Tok_Out,             -- OUT          Eterm, Sterm
 143       Tok_Record,          -- RECORD       Eterm, Sterm
 144       Tok_Renames,         -- RENAMES      Eterm, Sterm
 145       Tok_Reverse,         -- REVERSE      Eterm, Sterm
 146       Tok_Some,            -- SOME         Eterm, Sterm
 147       Tok_Tagged,          -- TAGGED       Eterm, Sterm
 148       Tok_Then,            -- THEN         Eterm, Sterm
 149
 150       Tok_Less_Less,       -- <<           Eterm, Sterm, After_SM
 151
 152       Tok_Abort,           -- ABORT        Eterm, Sterm, After_SM
 153       Tok_Accept,          -- ACCEPT       Eterm, Sterm, After_SM
 154       Tok_Case,            -- CASE         Eterm, Sterm, After_SM
 155       Tok_Delay,           -- DELAY        Eterm, Sterm, After_SM
 156       Tok_Else,            -- ELSE         Eterm, Sterm, After_SM
 157       Tok_Elsif,           -- ELSIF        Eterm, Sterm, After_SM
 158       Tok_End,             -- END          Eterm, Sterm, After_SM
 159       Tok_Exception,       -- EXCEPTION    Eterm, Sterm, After_SM
 160       Tok_Exit,            -- EXIT         Eterm, Sterm, After_SM
 161       Tok_Goto,            -- GOTO         Eterm, Sterm, After_SM
 162       Tok_If,              -- IF           Eterm, Sterm, After_SM
 163       Tok_Pragma,          -- PRAGMA       Eterm, Sterm, After_SM
 164       Tok_Requeue,         -- REQUEUE      Eterm, Sterm, After_SM
 165       Tok_Return,          -- RETURN       Eterm, Sterm, After_SM
 166       Tok_Select,          -- SELECT       Eterm, Sterm, After_SM
 167       Tok_Terminate,       -- TERMINATE    Eterm, Sterm, After_SM
 168       Tok_Until,           -- UNTIL        Eterm, Sterm, After_SM
 169       Tok_When,            -- WHEN         Eterm, Sterm, After_SM
 170
 171       Tok_Begin,           -- BEGIN        Eterm, Sterm, After_SM, Labeled_Stmt
 172       Tok_Declare,         -- DECLARE      Eterm, Sterm, After_SM, Labeled_Stmt
 173       Tok_For,             -- FOR          Eterm, Sterm, After_SM, Labeled_Stmt
 174       Tok_Loop,            -- LOOP         Eterm, Sterm, After_SM, Labeled_Stmt
 175       Tok_While,           -- WHILE        Eterm, Sterm, After_SM, Labeled_Stmt
 176
 177       Tok_Entry,           -- ENTRY        Eterm, Sterm, Declk, Deckn, After_SM
 178       Tok_Protected,       -- PROTECTED    Eterm, Sterm, Declk, Deckn, After_SM
 179       Tok_Task,            -- TASK         Eterm, Sterm, Declk, Deckn, After_SM
 180       Tok_Type,            -- TYPE         Eterm, Sterm, Declk, Deckn, After_SM
 181       Tok_Subtype,         -- SUBTYPE      Eterm, Sterm, Declk, Deckn, After_SM
 182       Tok_Overriding,      -- OVERRIDING   Eterm, Sterm, Declk, Declk, After_SM
 183       Tok_Synchronized,    -- SYNCHRONIZED Eterm, Sterm, Declk, Deckn, After_SM
 184       Tok_Use,             -- USE          Eterm, Sterm, Declk, Deckn, After_SM
 185
 186       Tok_Function,        -- FUNCTION     Eterm, Sterm, Cunit, Declk, After_SM
 187       Tok_Generic,         -- GENERIC      Eterm, Sterm, Cunit, Declk, After_SM
 188       Tok_Package,         -- PACKAGE      Eterm, Sterm, Cunit, Declk, After_SM
 189       Tok_Procedure,       -- PROCEDURE    Eterm, Sterm, Cunit, Declk, After_SM
 190
 191       Tok_Private,         -- PRIVATE      Eterm, Sterm, Cunit, After_SM
 192       Tok_With,            -- WITH         Eterm, Sterm, Cunit, After_SM
 193       Tok_Separate,        -- SEPARATE     Eterm, Sterm, Cunit, After_SM
 194
 195       Tok_EOF,             -- End of file  Eterm, Sterm, Cterm, After_SM
 196
 197       Tok_Semicolon,       -- ;            Eterm, Sterm, Cterm
 198
 199       Tok_Arrow,           -- =>           Sterm, Cterm, Chtok
 200
 201       Tok_Vertical_Bar,    -- |            Cterm, Sterm, Chtok
 202
 203       Tok_Dot_Dot,         -- ..           Sterm, Chtok
 204
 205       Tok_Project,
 206       Tok_Extends,
 207       Tok_External,
 208       Tok_External_As_List,
 209       --  These four entries represent keywords for the project file language
 210       --  and can be returned only in the case of scanning project files.
 211
 212       Tok_Comment,
 213       --  This entry is used when scanning project files (where it represents
 214       --  an entire comment), and in preprocessing with the -C switch set
 215       --  (where it represents just the "--" of a comment). For the project
 216       --  file case, the text of the comment is stored in Comment_Id.
 217
 218       Tok_End_Of_Line,
 219       --  Represents an end of line. Not used during normal compilation scans
 220       --  where end of line is ignored. Active for preprocessor scanning.
 221
 222       Tok_Special,
 223       --  Special character used by the preprocessor. The character itself is
 224       --  stored in Special_Character below.
 225
 226       No_Token);
 227       --  No_Token is used for initializing Token values to indicate that
 228       --  no value has been set yet.
 229
 230    function Keyword_Name (Token : Token_Type) return Name_Id;
 231    --  Given a token that is a reserved word, return the corresponding Name_Id
 232    --  in lower case. E.g. Keyword_Name (Tok_Begin) = Name_Find ("begin").
 233    --  It is an error to pass any other kind of token.
 234
 235    --  Note: in the RM, operator symbol is a special case of string literal.
 236    --  We distinguish at the lexical level in this compiler, since there are
 237    --  many syntactic situations in which only an operator symbol is allowed.
 238
 239    --  The following subtype declarations group the token types into classes.
 240    --  These are used for class tests in the parser.
 241
 242    subtype Token_Class_Numeric_Literal is
 243      Token_Type range Tok_Integer_Literal .. Tok_Real_Literal;
 244    --  Numeric literal
 245
 246    subtype Token_Class_Literal is
 247      Token_Type range Tok_Integer_Literal .. Tok_Operator_Symbol;
 248    --  Literal
 249
 250    subtype Token_Class_Lit_Or_Name is
 251      Token_Type range Tok_Integer_Literal .. Tok_Identifier;
 252
 253    subtype Token_Class_Binary_Addop is
 254      Token_Type range Tok_Ampersand .. Tok_Plus;
 255    --  Binary adding operator (& + -)
 256
 257    subtype Token_Class_Unary_Addop is
 258      Token_Type range Tok_Minus .. Tok_Plus;
 259    --  Unary adding operator (+ -)
 260
 261    subtype Token_Class_Mulop is
 262      Token_Type range Tok_Asterisk .. Tok_Slash;
 263    --  Multiplying operator
 264
 265    subtype Token_Class_Logop is
 266      Token_Type range Tok_And .. Tok_Xor;
 267    --  Logical operator (and, or, xor)
 268
 269    subtype Token_Class_Relop is
 270      Token_Type range Tok_Less .. Tok_Box;
 271    --  Relational operator (= /= < <= > >= not, in plus <> to catch misuse
 272    --  of Pascal style not equal operator).
 273
 274    subtype Token_Class_Name is
 275    Token_Type range Tok_Char_Literal .. Tok_At_Sign;
 276    --  First token of name (4.1),
 277    --    (identifier, char literal, operator symbol)
 278    --  Includes '@' after Ada2012 corrigendum.
 279
 280    subtype Token_Class_Desig is
 281      Token_Type range Tok_Operator_Symbol .. Tok_At_Sign;
 282    --  Token which can be a Designator (identifier, operator symbol)
 283
 284    subtype Token_Class_Namext is
 285      Token_Type range Tok_Dot .. Tok_Left_Paren;
 286    --  Name extension tokens. These are tokens which can appear immediately
 287    --  after a name to extend it recursively (period, quote, left paren)
 288
 289    subtype Token_Class_Consk is
 290      Token_Type range Tok_Left_Paren .. Tok_Range;
 291    --  Keywords which can start constraint
 292    --    (left paren, delta, digits, range)
 293
 294    subtype Token_Class_Eterm is
 295      Token_Type range Tok_Colon_Equal .. Tok_Semicolon;
 296    --  Expression terminators. These tokens can never appear within a simple
 297    --  expression. This is used for error recovery purposes (if we encounter
 298    --  an error in an expression, we simply scan to the next Eterm token).
 299
 300    subtype Token_Class_Sterm is
 301      Token_Type range Tok_Delta .. Tok_Dot_Dot;
 302    --  Simple_Expression terminators. A Simple_Expression must be followed
 303    --  by a token in this class, or an error message is issued complaining
 304    --  about a missing binary operator.
 305
 306    subtype Token_Class_Atkwd is
 307      Token_Type range Tok_Delta .. Tok_Range;
 308    --  Attribute keywords. This class includes keywords which can be used
 309    --  as an Attribute_Designator, namely DELTA, DIGITS and RANGE
 310
 311    subtype Token_Class_Cterm is
 312      Token_Type range Tok_EOF .. Tok_Vertical_Bar;
 313    --  Choice terminators. These tokens terminate a choice. This is used for
 314    --  error recovery purposes (if we encounter an error in a Choice, we
 315    --  simply scan to the next Cterm token).
 316
 317    subtype Token_Class_Chtok is
 318      Token_Type range Tok_Arrow .. Tok_Dot_Dot;
 319    --  Choice tokens. These tokens signal a choice when used in an Aggregate
 320
 321    subtype Token_Class_Cunit is
 322      Token_Type range Tok_Function .. Tok_Separate;
 323    --  Tokens which can begin a compilation unit
 324
 325    subtype Token_Class_Declk is
 326      Token_Type range Tok_Entry .. Tok_Procedure;
 327    --  Keywords which start a declaration
 328
 329    subtype Token_Class_Deckn is
 330      Token_Type range Tok_Entry .. Tok_Use;
 331    --  Keywords which start a declaration but can't start a compilation unit
 332
 333    subtype Token_Class_After_SM is
 334      Token_Type range Tok_Less_Less .. Tok_EOF;
 335    --  Tokens which always, or almost always, appear after a semicolon. Used
 336    --  in the Resync_Past_Semicolon routine to avoid gobbling up stuff when
 337    --  a semicolon is missing. Of significance only for error recovery.
 338
 339    subtype Token_Class_Labeled_Stmt is
 340      Token_Type range Tok_Begin .. Tok_While;
 341    --  Tokens which start labeled statements
 342
 343    type Token_Flag_Array is array (Token_Type) of Boolean;
 344    Is_Reserved_Keyword : constant Token_Flag_Array :=
 345                            Token_Flag_Array'
 346                              (Tok_Mod      .. Tok_Rem      => True,
 347                               Tok_New      .. Tok_Null     => True,
 348                               Tok_Delta    .. Tok_Range    => True,
 349                               Tok_And      .. Tok_Xor      => True,
 350                               Tok_In       .. Tok_Not      => True,
 351                               Tok_Abstract .. Tok_Then     => True,
 352                               Tok_Abort    .. Tok_Separate => True,
 353                               others                       => False);
 354    --  Flag array used to test for reserved word
 355
 356    procedure Initialize_Ada_Keywords;
 357    --  Set up Token_Type values in Names table entries for Ada reserved
 358    --  words. This ignores Ada_Version; Ada_Version is taken into account in
 359    --  Snames.Is_Keyword_Name.
 360
 361    --------------------------
 362    -- Scan State Variables --
 363    --------------------------
 364
 365    --  Note: these variables can only be referenced during the parsing of a
 366    --  file. Reference to any of them from Sem or the expander is wrong.
 367
 368    --  These variables are initialized by Scn.Initialize_Scanner, and should
 369    --  not be referenced before such a call, except for saving and restoring
 370    --  them.
 371
 372    Scan_Ptr : Source_Ptr := No_Location;
 373    --  Current scan pointer location. After a call to Scan, this points
 374    --  just past the end of the token just scanned.
 375
 376    Token : Token_Type := No_Token;
 377    --  Type of current token
 378
 379    Token_Ptr : Source_Ptr := No_Location;
 380    --  Pointer to first character of current token
 381
 382    Current_Line_Start : Source_Ptr := No_Location;
 383    --  Pointer to first character of line containing current token
 384
 385    Start_Column : Column_Number := No_Column_Number;
 386    --  Starting column number (zero origin) of the first non-blank character
 387    --  on the line containing the current token. This is used for error
 388    --  recovery circuits which depend on looking at the column line up.
 389
 390    Type_Token_Location : Source_Ptr := No_Location;
 391    --  Within a type declaration, gives the location of the TYPE keyword that
 392    --  opened the type declaration. Used in checking the end column of a record
 393    --  declaration, which can line up either with the TYPE keyword, or with the
 394    --  start of the line containing the RECORD keyword.
 395
 396    Checksum : Word := 0;
 397    --  Used to accumulate a CRC representing the tokens in the source
 398    --  file being compiled. This CRC includes only program tokens, and
 399    --  excludes comments.
 400
 401    Limited_Checksum : Word := 0;
 402    --  Used to accumulate a CRC representing significant tokens in the
 403    --  limited view of a package, i.e. visible type names and related
 404    --  tagged indicators.
 405
 406    First_Non_Blank_Location : Source_Ptr := No_Location;
 407    --  Location of first non-blank character on the line containing the
 408    --  current token (i.e. the location of the character whose column number
 409    --  is stored in Start_Column).
 410
 411    Token_Node : Node_Id := Empty;
 412    --  Node table Id for the current token. This is set only if the current
 413    --  token is one for which the scanner constructs a node (i.e. it is an
 414    --  identifier, operator symbol, or literal). For other token types,
 415    --  Token_Node is undefined.
 416
 417    Token_Name : Name_Id := No_Name;
 418    --  For identifiers, this is set to the Name_Id of the identifier scanned.
 419    --  For all other tokens, Token_Name is set to Error_Name. Note that it
 420    --  would be possible for the caller to extract this information from
 421    --  Token_Node. We set Token_Name separately for two reasons. First it
 422    --  allows a quicker test for a specific identifier. Second, it allows
 423    --  a version of the parser to be built that does not build tree nodes,
 424    --  usable as a syntax checker.
 425
 426    Prev_Token : Token_Type := No_Token;
 427    --  Type of previous token
 428
 429    Prev_Token_Ptr : Source_Ptr;
 430    --  Pointer to first character of previous token
 431
 432    Version_To_Be_Found : Boolean;
 433    --  This flag is True if the scanner is still looking for an RCS version
 434    --  number in a comment. Normally it is initialized to False so that this
 435    --  circuit is not activated. If the -dv switch is set, then this flag is
 436    --  initialized to True, and then reset when the version number is found.
 437    --  We do things this way to minimize the impact on comment scanning.
 438
 439    Character_Code : Char_Code;
 440    --  Valid only when Token is Tok_Char_Literal. Contains the value of the
 441    --  scanned literal.
 442
 443    Real_Literal_Value : Ureal;
 444    --  Valid only when Token is Tok_Real_Literal. Contains the value of the
 445    --  scanned literal.
 446
 447    Int_Literal_Value : Uint;
 448    --  Valid only when Token = Tok_Integer_Literal, and we are not in
 449    --  syntax-only mode. Contains the value of the scanned literal.
 450
 451    Based_Literal_Uses_Colon : Boolean;
 452    --  Valid only when Token = Tok_Integer_Literal or Tok_Real_Literal. Set
 453    --  True only for the case of a based literal using ':' instead of '#'.
 454
 455    String_Literal_Id : String_Id;
 456    --  Valid only when Token = Tok_String_Literal or Tok_Operator_Symbol.
 457    --  Contains the Id for currently scanned string value.
 458
 459    Wide_Character_Found : Boolean := False;
 460    --  Valid only when Token = Tok_String_Literal. Set True if wide character
 461    --  found (i.e. a character that does not fit in Character, but fits in
 462    --  Wide_Wide_Character).
 463
 464    Wide_Wide_Character_Found : Boolean := False;
 465    --  Valid only when Token = Tok_String_Literal. Set True if wide wide
 466    --  character found (i.e. a character that does not fit in Character or
 467    --  Wide_Character).
 468
 469    subtype Special_Preprocessor_Character is Character with
 470      Predicate => Special_Preprocessor_Character in '#' | '$';
 471    Special_Character : Special_Preprocessor_Character;
 472
 473    Comment_Id : Name_Id := No_Name;
 474    --  Valid only when Token = Tok_Comment. Store the string that follows
 475    --  the "--" of a comment when scanning project files.
 476    --
 477    --  Is it really right for this to be a Name rather than a String, what
 478    --  about the case of Wide_Wide_Characters???
 479
 480    Inside_Depends : Boolean := False;
 481    --  True while parsing the argument of a Depends or Refined_Depends pragma
 482    --  or aspect. Used to allow/require nonstandard style rules for =>+ with
 483    --  -gnatyt.
 484
 485    Inside_Interpolated_String_Expression : Boolean := False;
 486    --  True while parsing an interpolated string expression
 487
 488    Inside_Interpolated_String_Literal : Boolean := False;
 489    --  True while parsing an interpolated string literal
 490
 491    Inside_If_Expression : Nat := 0;
 492    --  This is a counter that is set non-zero while scanning out an if
 493    --  expression (incremented on entry, decremented on exit). It is used to
 494    --  disconnect format checks that normally apply to keywords THEN, ELSE etc.
 495
 496    Inside_Pragma : Boolean := False;
 497    --  True within a pragma. Used to avoid complaining about reserved words
 498    --  within pragmas (see Scan_Reserved_Identifier).
 499
 500    --------------------------------------------------------
 501    -- Procedures for Saving and Restoring the Scan State --
 502    --------------------------------------------------------
 503
 504    --  The following procedures can be used to save and restore the entire
 505    --  scan state. They are used in cases where it is necessary to backup
 506    --  the scan during the parse.
 507
 508    type Saved_Scan_State is private;
 509    --  Used for saving and restoring the scan state
 510
 511    procedure Save_Scan_State (Saved_State : out Saved_Scan_State);
 512    pragma Inline (Save_Scan_State);
 513    --  Saves the current scan state for possible later restoration. Note that
 514    --  there is no harm in saving the state and then never restoring it.
 515
 516    procedure Restore_Scan_State (Saved_State : Saved_Scan_State);
 517    pragma Inline (Restore_Scan_State);
 518    --  Restores a scan state saved by a call to Save_Scan_State.
 519    --  The saved scan state must refer to the current source file.
 520
 521 private
 522    type Saved_Scan_State is record
 523       Save_Scan_Ptr                 : Source_Ptr;
 524       Save_Token                    : Token_Type;
 525       Save_Token_Ptr                : Source_Ptr;
 526       Save_Current_Line_Start       : Source_Ptr;
 527       Save_Start_Column             : Column_Number;
 528       Save_Checksum                 : Word;
 529       Save_First_Non_Blank_Location : Source_Ptr;
 530       Save_Token_Node               : Node_Id;
 531       Save_Token_Name               : Name_Id;
 532       Save_Prev_Token               : Token_Type;
 533       Save_Prev_Token_Ptr           : Source_Ptr;
 534    end record;
 535
 536 end Scans;