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) 1992-2016, 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.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 with Namet;  use Namet;
  33 with Types;  use Types;
  34 with Uintp;  use Uintp;
  35 with Urealp; use Urealp;
  36
  37 package Scans is
  38
  39 --  The scanner maintains a current state in the global variables defined
  40 --  in this package. The call to the Scan routine advances this state to
  41 --  the next token. The state is initialized by the call to one of the
  42 --  initialization routines in Sinput.
  43
  44    --  The following type is used to identify token types returned by Scan.
  45    --  The class column in this table indicates the token classes which
  46    --  apply to the token, as defined by subsequent subtype declarations.
  47
  48    type Token_Type is (
  49
  50       --  Token name          Token type   Class(es)
  51
  52       Tok_Integer_Literal, -- numeric lit  Literal, Lit_Or_Name
  53
  54       Tok_Real_Literal,    -- numeric lit  Literal, Lit_Or_Name
  55
  56       Tok_String_Literal,  -- string lit   Literal. Lit_Or_Name
  57
  58       Tok_Char_Literal,    -- char lit     Name, Literal. Lit_Or_Name
  59
  60       Tok_Operator_Symbol, -- op symbol    Name, Literal, Lit_Or_Name, Desig
  61
  62       Tok_Identifier,      -- identifier   Name, Lit_Or_Name, Desig
  63
  64       Tok_At_Sign,         -- @  AI12-0125-3 : target name
  65
  66       Tok_Double_Asterisk, -- **
  67
  68       Tok_Ampersand,       -- &            Binary_Addop
  69       Tok_Minus,           -- -            Binary_Addop, Unary_Addop
  70       Tok_Plus,            -- +            Binary_Addop, Unary_Addop
  71
  72       Tok_Asterisk,        -- *            Mulop
  73       Tok_Mod,             -- MOD          Mulop
  74       Tok_Rem,             -- REM          Mulop
  75       Tok_Slash,           -- /            Mulop
  76
  77       Tok_New,             -- NEW
  78
  79       Tok_Abs,             -- ABS
  80       Tok_Others,          -- OTHERS
  81       Tok_Null,            -- NULL
  82
  83       --  Note: Tok_Raise is in no categories now, it used to be Cterm, Eterm,
  84       --  After_SM, but now that Ada 2012 has added raise expressions, the
  85       --  raise token can appear anywhere. Note in particular that Tok_Raise
  86       --  being in Eterm stopped the parser from recognizing "return raise
  87       --  exception-name". This degrades error recovery slightly, and perhaps
  88       --  we could do better, but not worth the effort.
  89
  90       Tok_Raise,           -- RAISE
  91
  92       Tok_Dot,             -- .            Namext
  93       Tok_Apostrophe,      -- '            Namext
  94
  95       Tok_Left_Paren,      -- (            Namext, Consk
  96
  97       Tok_Delta,           -- DELTA        Atkwd, Sterm, Consk
  98       Tok_Digits,          -- DIGITS       Atkwd, Sterm, Consk
  99       Tok_Range,           -- RANGE        Atkwd, Sterm, Consk
 100
 101       Tok_Right_Paren,     -- )            Sterm
 102       Tok_Comma,           -- ,            Sterm
 103
 104       Tok_And,             -- AND          Logop, Sterm
 105       Tok_Or,              -- OR           Logop, Sterm
 106       Tok_Xor,             -- XOR          Logop, Sterm
 107
 108       Tok_Less,            -- <            Relop, Sterm
 109       Tok_Equal,           -- =            Relop, Sterm
 110       Tok_Greater,         -- >            Relop, Sterm
 111       Tok_Not_Equal,       -- /=           Relop, Sterm
 112       Tok_Greater_Equal,   -- >=           Relop, Sterm
 113       Tok_Less_Equal,      -- <=           Relop, Sterm
 114
 115       Tok_In,              -- IN           Relop, Sterm
 116       Tok_Not,             -- NOT          Relop, Sterm
 117
 118       Tok_Box,             -- <>           Relop, Eterm, Sterm
 119       Tok_Colon_Equal,     -- :=           Eterm, Sterm
 120       Tok_Colon,           -- :            Eterm, Sterm
 121       Tok_Greater_Greater, -- >>           Eterm, Sterm
 122
 123       Tok_Abstract,        -- ABSTRACT     Eterm, Sterm
 124       Tok_Access,          -- ACCESS       Eterm, Sterm
 125       Tok_Aliased,         -- ALIASED      Eterm, Sterm
 126       Tok_All,             -- ALL          Eterm, Sterm
 127       Tok_Array,           -- ARRAY        Eterm, Sterm
 128       Tok_At,              -- AT           Eterm, Sterm
 129       Tok_Body,            -- BODY         Eterm, Sterm
 130       Tok_Constant,        -- CONSTANT     Eterm, Sterm
 131       Tok_Do,              -- DO           Eterm, Sterm
 132       Tok_Is,              -- IS           Eterm, Sterm
 133       Tok_Interface,       -- INTERFACE    Eterm, Sterm
 134       Tok_Limited,         -- LIMITED      Eterm, Sterm
 135       Tok_Of,              -- OF           Eterm, Sterm
 136       Tok_Out,             -- OUT          Eterm, Sterm
 137       Tok_Record,          -- RECORD       Eterm, Sterm
 138       Tok_Renames,         -- RENAMES      Eterm, Sterm
 139       Tok_Reverse,         -- REVERSE      Eterm, Sterm
 140       Tok_Some,            -- SOME         Eterm, Sterm
 141       Tok_Tagged,          -- TAGGED       Eterm, Sterm
 142       Tok_Then,            -- THEN         Eterm, Sterm
 143
 144       Tok_Less_Less,       -- <<           Eterm, Sterm, After_SM
 145
 146       Tok_Abort,           -- ABORT        Eterm, Sterm, After_SM
 147       Tok_Accept,          -- ACCEPT       Eterm, Sterm, After_SM
 148       Tok_Case,            -- CASE         Eterm, Sterm, After_SM
 149       Tok_Delay,           -- DELAY        Eterm, Sterm, After_SM
 150       Tok_Else,            -- ELSE         Eterm, Sterm, After_SM
 151       Tok_Elsif,           -- ELSIF        Eterm, Sterm, After_SM
 152       Tok_End,             -- END          Eterm, Sterm, After_SM
 153       Tok_Exception,       -- EXCEPTION    Eterm, Sterm, After_SM
 154       Tok_Exit,            -- EXIT         Eterm, Sterm, After_SM
 155       Tok_Goto,            -- GOTO         Eterm, Sterm, After_SM
 156       Tok_If,              -- IF           Eterm, Sterm, After_SM
 157       Tok_Pragma,          -- PRAGMA       Eterm, Sterm, After_SM
 158       Tok_Requeue,         -- REQUEUE      Eterm, Sterm, After_SM
 159       Tok_Return,          -- RETURN       Eterm, Sterm, After_SM
 160       Tok_Select,          -- SELECT       Eterm, Sterm, After_SM
 161       Tok_Terminate,       -- TERMINATE    Eterm, Sterm, After_SM
 162       Tok_Until,           -- UNTIL        Eterm, Sterm, After_SM
 163       Tok_When,            -- WHEN         Eterm, Sterm, After_SM
 164
 165       Tok_Begin,           -- BEGIN        Eterm, Sterm, After_SM, Labeled_Stmt
 166       Tok_Declare,         -- DECLARE      Eterm, Sterm, After_SM, Labeled_Stmt
 167       Tok_For,             -- FOR          Eterm, Sterm, After_SM, Labeled_Stmt
 168       Tok_Loop,            -- LOOP         Eterm, Sterm, After_SM, Labeled_Stmt
 169       Tok_While,           -- WHILE        Eterm, Sterm, After_SM, Labeled_Stmt
 170
 171       Tok_Entry,           -- ENTRY        Eterm, Sterm, Declk, Deckn, After_SM
 172       Tok_Protected,       -- PROTECTED    Eterm, Sterm, Declk, Deckn, After_SM
 173       Tok_Task,            -- TASK         Eterm, Sterm, Declk, Deckn, After_SM
 174       Tok_Type,            -- TYPE         Eterm, Sterm, Declk, Deckn, After_SM
 175       Tok_Subtype,         -- SUBTYPE      Eterm, Sterm, Declk, Deckn, After_SM
 176       Tok_Overriding,      -- OVERRIDING   Eterm, Sterm, Declk, Declk, After_SM
 177       Tok_Synchronized,    -- SYNCHRONIZED Eterm, Sterm, Declk, Deckn, After_SM
 178       Tok_Use,             -- USE          Eterm, Sterm, Declk, Deckn, After_SM
 179
 180       Tok_Function,        -- FUNCTION     Eterm, Sterm, Cunit, Declk, After_SM
 181       Tok_Generic,         -- GENERIC      Eterm, Sterm, Cunit, Declk, After_SM
 182       Tok_Package,         -- PACKAGE      Eterm, Sterm, Cunit, Declk, After_SM
 183       Tok_Procedure,       -- PROCEDURE    Eterm, Sterm, Cunit, Declk, After_SM
 184
 185       Tok_Private,         -- PRIVATE      Eterm, Sterm, Cunit, After_SM
 186       Tok_With,            -- WITH         Eterm, Sterm, Cunit, After_SM
 187       Tok_Separate,        -- SEPARATE     Eterm, Sterm, Cunit, After_SM
 188
 189       Tok_EOF,             -- End of file  Eterm, Sterm, Cterm, After_SM
 190
 191       Tok_Semicolon,       -- ;            Eterm, Sterm, Cterm
 192
 193       Tok_Arrow,           -- =>           Sterm, Cterm, Chtok
 194
 195       Tok_Vertical_Bar,    -- |            Cterm, Sterm, Chtok
 196
 197       Tok_Dot_Dot,         -- ..           Sterm, Chtok
 198
 199       Tok_Project,
 200       Tok_Extends,
 201       Tok_External,
 202       Tok_External_As_List,
 203       --  These four entries represent keywords for the project file language
 204       --  and can be returned only in the case of scanning project files.
 205
 206       Tok_Comment,
 207       --  This entry is used when scanning project files (where it represents
 208       --  an entire comment), and in preprocessing with the -C switch set
 209       --  (where it represents just the "--" of a comment). For the project
 210       --  file case, the text of the comment is stored in Comment_Id.
 211
 212       Tok_End_Of_Line,
 213       --  Represents an end of line. Not used during normal compilation scans
 214       --  where end of line is ignored. Active for preprocessor scanning and
 215       --  also when scanning project files (where it is needed because of ???)
 216
 217       Tok_Special,
 218       --  AI12-0125-03 : target name as abbreviation for LHS
 219
 220       --  Otherwise used only in preprocessor scanning (to represent one of
 221       --  the characters '#', '$', '?', '@', '`', '\', '^', '~', or '_'. The
 222       --  character value itself is stored in Scans.Special_Character.
 223
 224       Tok_SPARK_Hide,
 225       --  HIDE directive in SPARK
 226
 227       No_Token);
 228       --  No_Token is used for initializing Token values to indicate that
 229       --  no value has been set yet.
 230
 231    function Keyword_Name (Token : Token_Type) return Name_Id;
 232    --  Given a token that is a reserved word, return the corresponding Name_Id
 233    --  in lower case. E.g. Keyword_Name (Tok_Begin) = Name_Find ("begin").
 234    --  It is an error to pass any other kind of token.
 235
 236    --  Note: in the RM, operator symbol is a special case of string literal.
 237    --  We distinguish at the lexical level in this compiler, since there are
 238    --  many syntactic situations in which only an operator symbol is allowed.
 239
 240    --  The following subtype declarations group the token types into classes.
 241    --  These are used for class tests in the parser.
 242
 243    subtype Token_Class_Numeric_Literal is
 244      Token_Type range Tok_Integer_Literal .. Tok_Real_Literal;
 245    --  Numeric literal
 246
 247    subtype Token_Class_Literal is
 248      Token_Type range Tok_Integer_Literal .. Tok_Operator_Symbol;
 249    --  Literal
 250
 251    subtype Token_Class_Lit_Or_Name is
 252      Token_Type range Tok_Integer_Literal .. Tok_Identifier;
 253
 254    subtype Token_Class_Binary_Addop is
 255      Token_Type range Tok_Ampersand .. Tok_Plus;
 256    --  Binary adding operator (& + -)
 257
 258    subtype Token_Class_Unary_Addop is
 259      Token_Type range Tok_Minus .. Tok_Plus;
 260    --  Unary adding operator (+ -)
 261
 262    subtype Token_Class_Mulop is
 263      Token_Type range Tok_Asterisk .. Tok_Slash;
 264    --  Multiplying operator
 265
 266    subtype Token_Class_Logop is
 267      Token_Type range Tok_And .. Tok_Xor;
 268    --  Logical operator (and, or, xor)
 269
 270    subtype Token_Class_Relop is
 271      Token_Type range Tok_Less .. Tok_Box;
 272    --  Relational operator (= /= < <= > >= not, in plus <> to catch misuse
 273    --  of Pascal style not equal operator).
 274
 275    subtype Token_Class_Name is
 276    Token_Type range Tok_Char_Literal .. Tok_At_Sign;
 277    --  First token of name (4.1),
 278    --    (identifier, char literal, operator symbol)
 279    --  Includes '@' after Ada2012 corrigendum.
 280
 281    subtype Token_Class_Desig is
 282      Token_Type range Tok_Operator_Symbol .. Tok_At_Sign;
 283    --  Token which can be a Designator (identifier, operator symbol)
 284
 285    subtype Token_Class_Namext is
 286      Token_Type range Tok_Dot .. Tok_Left_Paren;
 287    --  Name extension tokens. These are tokens which can appear immediately
 288    --  after a name to extend it recursively (period, quote, left paren)
 289
 290    subtype Token_Class_Consk is
 291      Token_Type range Tok_Left_Paren .. Tok_Range;
 292    --  Keywords which can start constraint
 293    --    (left paren, delta, digits, range)
 294
 295    subtype Token_Class_Eterm is
 296      Token_Type range Tok_Colon_Equal .. Tok_Semicolon;
 297    --  Expression terminators. These tokens can never appear within a simple
 298    --  expression. This is used for error recovery purposes (if we encounter
 299    --  an error in an expression, we simply scan to the next Eterm token).
 300
 301    subtype Token_Class_Sterm is
 302      Token_Type range Tok_Delta .. Tok_Dot_Dot;
 303    --  Simple_Expression terminators. A Simple_Expression must be followed
 304    --  by a token in this class, or an error message is issued complaining
 305    --  about a missing binary operator.
 306
 307    subtype Token_Class_Atkwd is
 308      Token_Type range Tok_Delta .. Tok_Range;
 309    --  Attribute keywords. This class includes keywords which can be used
 310    --  as an Attribute_Designator, namely DELTA, DIGITS and RANGE
 311
 312    subtype Token_Class_Cterm is
 313      Token_Type range Tok_EOF .. Tok_Vertical_Bar;
 314    --  Choice terminators. These tokens terminate a choice. This is used for
 315    --  error recovery purposes (if we encounter an error in a Choice, we
 316    --  simply scan to the next Cterm token).
 317
 318    subtype Token_Class_Chtok is
 319      Token_Type range Tok_Arrow .. Tok_Dot_Dot;
 320    --  Choice tokens. These tokens signal a choice when used in an Aggregate
 321
 322    subtype Token_Class_Cunit is
 323      Token_Type range Tok_Function .. Tok_Separate;
 324    --  Tokens which can begin a compilation unit
 325
 326    subtype Token_Class_Declk is
 327      Token_Type range Tok_Entry .. Tok_Procedure;
 328    --  Keywords which start a declaration
 329
 330    subtype Token_Class_Deckn is
 331      Token_Type range Tok_Entry .. Tok_Use;
 332    --  Keywords which start a declaration but can't start a compilation unit
 333
 334    subtype Token_Class_After_SM is
 335      Token_Type range Tok_Less_Less .. Tok_EOF;
 336    --  Tokens which always, or almost always, appear after a semicolon. Used
 337    --  in the Resync_Past_Semicolon routine to avoid gobbling up stuff when
 338    --  a semicolon is missing. Of significance only for error recovery.
 339
 340    subtype Token_Class_Labeled_Stmt is
 341      Token_Type range Tok_Begin .. Tok_While;
 342    --  Tokens which start labeled statements
 343
 344    type Token_Flag_Array is array (Token_Type) of Boolean;
 345    Is_Reserved_Keyword : constant Token_Flag_Array :=
 346                            Token_Flag_Array'
 347                              (Tok_Mod      .. Tok_Rem      => True,
 348                               Tok_New      .. Tok_Null     => True,
 349                               Tok_Delta    .. Tok_Range    => True,
 350                               Tok_And      .. Tok_Xor      => True,
 351                               Tok_In       .. Tok_Not      => True,
 352                               Tok_Abstract .. Tok_Then     => True,
 353                               Tok_Abort    .. Tok_Separate => True,
 354                               others                       => False);
 355    --  Flag array used to test for reserved word
 356
 357    procedure Initialize_Ada_Keywords;
 358    --  Set up Token_Type values in Names table entries for Ada reserved
 359    --  words. This ignores Ada_Version; Ada_Version is taken into account in
 360    --  Snames.Is_Keyword_Name.
 361
 362    --------------------------
 363    -- Scan State Variables --
 364    --------------------------
 365
 366    --  Note: these variables can only be referenced during the parsing of a
 367    --  file. Reference to any of them from Sem or the expander is wrong.
 368
 369    --  These variables are initialized as required by Scn.Initialize_Scanner,
 370    --  and should not be referenced before such a call. However, there are
 371    --  situations in which these variables are saved and restored, and this
 372    --  may happen before the first Initialize_Scanner call, resulting in the
 373    --  assignment of invalid values. To avoid this, and allow building with
 374    --  the -gnatVa switch, we initialize some variables to known valid values.
 375
 376    Scan_Ptr : Source_Ptr := No_Location; -- init for -gnatVa
 377    --  Current scan pointer location. After a call to Scan, this points
 378    --  just past the end of the token just scanned.
 379
 380    Token : Token_Type := No_Token; -- init for -gnatVa
 381    --  Type of current token
 382
 383    Token_Ptr : Source_Ptr := No_Location; -- init for -gnatVa
 384    --  Pointer to first character of current token
 385
 386    Current_Line_Start : Source_Ptr := No_Location; -- init for -gnatVa
 387    --  Pointer to first character of line containing current token
 388
 389    Start_Column : Column_Number := No_Column_Number; -- init for -gnatVa
 390    --  Starting column number (zero origin) of the first non-blank character
 391    --  on the line containing the current token. This is used for error
 392    --  recovery circuits which depend on looking at the column line up.
 393
 394    Type_Token_Location : Source_Ptr := No_Location; -- init for -gnatVa
 395    --  Within a type declaration, gives the location of the TYPE keyword that
 396    --  opened the type declaration. Used in checking the end column of a record
 397    --  declaration, which can line up either with the TYPE keyword, or with the
 398    --  start of the line containing the RECORD keyword.
 399
 400    Checksum : Word := 0; -- init for -gnatVa
 401    --  Used to accumulate a CRC representing the tokens in the source
 402    --  file being compiled. This CRC includes only program tokens, and
 403    --  excludes comments.
 404
 405    Limited_Checksum : Word := 0;
 406    --  Used to accumulate a CRC representing significant tokens in the
 407    --  limited view of a package, i.e. visible type names and related
 408    --  tagged indicators.
 409
 410    First_Non_Blank_Location : Source_Ptr := No_Location; -- init for -gnatVa
 411    --  Location of first non-blank character on the line containing the
 412    --  current token (i.e. the location of the character whose column number
 413    --  is stored in Start_Column).
 414
 415    Token_Node : Node_Id := Empty;
 416    --  Node table Id for the current token. This is set only if the current
 417    --  token is one for which the scanner constructs a node (i.e. it is an
 418    --  identifier, operator symbol, or literal). For other token types,
 419    --  Token_Node is undefined.
 420
 421    Token_Name : Name_Id := No_Name;
 422    --  For identifiers, this is set to the Name_Id of the identifier scanned.
 423    --  For all other tokens, Token_Name is set to Error_Name. Note that it
 424    --  would be possible for the caller to extract this information from
 425    --  Token_Node. We set Token_Name separately for two reasons. First it
 426    --  allows a quicker test for a specific identifier. Second, it allows
 427    --  a version of the parser to be built that does not build tree nodes,
 428    --  usable as a syntax checker.
 429
 430    Prev_Token : Token_Type := No_Token;
 431    --  Type of previous token
 432
 433    Prev_Token_Ptr : Source_Ptr;
 434    --  Pointer to first character of previous token
 435
 436    Version_To_Be_Found : Boolean;
 437    --  This flag is True if the scanner is still looking for an RCS version
 438    --  number in a comment. Normally it is initialized to False so that this
 439    --  circuit is not activated. If the -dv switch is set, then this flag is
 440    --  initialized to True, and then reset when the version number is found.
 441    --  We do things this way to minimize the impact on comment scanning.
 442
 443    Character_Code : Char_Code;
 444    --  Valid only when Token is Tok_Char_Literal. Contains the value of the
 445    --  scanned literal.
 446
 447    Real_Literal_Value : Ureal;
 448    --  Valid only when Token is Tok_Real_Literal, contains the value of the
 449    --  scanned literal.
 450
 451    Int_Literal_Value : Uint;
 452    --  Valid only when Token = Tok_Integer_Literal, contains the value of the
 453    --  scanned literal.
 454
 455    Based_Literal_Uses_Colon : Boolean;
 456    --  Valid only when Token = Tok_Integer_Literal or Tok_Real_Literal. Set
 457    --  True only for the case of a based literal using ':' instead of '#'.
 458
 459    String_Literal_Id : String_Id;
 460    --  Valid only when Token = Tok_String_Literal or Tok_Operator_Symbol.
 461    --  Contains the Id for currently scanned string value.
 462
 463    Wide_Character_Found : Boolean := False;
 464    --  Valid only when Token = Tok_String_Literal. Set True if wide character
 465    --  found (i.e. a character that does not fit in Character, but fits in
 466    --  Wide_Wide_Character).
 467
 468    Wide_Wide_Character_Found : Boolean := False;
 469    --  Valid only when Token = Tok_String_Literal. Set True if wide wide
 470    --  character found (i.e. a character that does not fit in Character or
 471    --  Wide_Character).
 472
 473    Special_Character : Character;
 474    --  AI12-0125-03 : '@' as target name is handled elsewhere.
 475    --  Valid only when Token = Tok_Special. Returns one of the characters
 476    --  '#', '$', '?', '`', '\', '^', '~', or '_'.
 477    --
 478    --  Why only this set? What about wide characters???
 479
 480    Comment_Id : Name_Id := No_Name;
 481    --  Valid only when Token = Tok_Comment. Store the string that follows
 482    --  the "--" of a comment when scanning project files.
 483    --
 484    --  Is it really right for this to be a Name rather than a String, what
 485    --  about the case of Wide_Wide_Characters???
 486
 487    Inside_Depends : Boolean := False;
 488    --  Flag set True for parsing the argument of a Depends pragma or aspect
 489    --  (used to allow/require non-standard style rules for =>+ with -gnatyt).
 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    --------------------------------------------------------
 497    -- Procedures for Saving and Restoring the Scan State --
 498    --------------------------------------------------------
 499
 500    --  The following procedures can be used to save and restore the entire
 501    --  scan state. They are used in cases where it is necessary to backup
 502    --  the scan during the parse.
 503
 504    type Saved_Scan_State is private;
 505    --  Used for saving and restoring the scan state
 506
 507    procedure Save_Scan_State (Saved_State : out Saved_Scan_State);
 508    pragma Inline (Save_Scan_State);
 509    --  Saves the current scan state for possible later restoration. Note that
 510    --  there is no harm in saving the state and then never restoring it.
 511
 512    procedure Restore_Scan_State (Saved_State : Saved_Scan_State);
 513    pragma Inline (Restore_Scan_State);
 514    --  Restores a scan state saved by a call to Save_Scan_State.
 515    --  The saved scan state must refer to the current source file.
 516
 517 private
 518    type Saved_Scan_State is record
 519       Save_Scan_Ptr                 : Source_Ptr;
 520       Save_Token                    : Token_Type;
 521       Save_Token_Ptr                : Source_Ptr;
 522       Save_Current_Line_Start       : Source_Ptr;
 523       Save_Start_Column             : Column_Number;
 524       Save_Checksum                 : Word;
 525       Save_First_Non_Blank_Location : Source_Ptr;
 526       Save_Token_Node               : Node_Id;
 527       Save_Token_Name               : Name_Id;
 528       Save_Prev_Token               : Token_Type;
 529       Save_Prev_Token_Ptr           : Source_Ptr;
 530    end record;
 531
 532 end Scans;