Delphi Magazine Collection 2001/Delphi Magazine Collection 20001 (2001).iso/DISKS/Issue70/alfresco/AARegex.pas

Pascal/Delphi Source File | 2001-05-08 | 39.3 KB | 1,286 lines

{*********************************************************}
{* AARegex                                               *}
{* Copyright (c) Julian M Bucknall 2001                  *}
{* All rights reserved.                                  *}
{*********************************************************}
{* Algorithms Alfresco: Regular expression classes       *}
{*********************************************************}

{Note: this unit is released as freeware. In other words, you are free
       to use this unit in your own applications, however I retain all
       copyright to the code. JMB}

unit AARegex;

interface

{Notes: these classes parse regular expressions that follow this
        grammar:

        <anchorexpr> ::= <expr> |
                         '^' <expr> |
                         <expr> '$' |
                         '^' <expr> '$'
        <expr> ::= <term> |
                   <term> '|' <expr>                 - alternation
        <term> ::= <factor> |
                   <factor><term>                    - concatenation
        <factor> ::= <atom> |
                     <atom> '?' |                    - zero or one
                     <atom> '*' |                    - zero or more
                     <atom> '+'                      - one or more
        <atom> ::= <char> |
                   '.' |                             - any char
                   '(' <expr> ') |                   - parentheses
                   '[' <charclass> ']' |             - normal class
                   '[^' <charclass> ']'              - negated class
        <charclass> ::= <charrange> |
                        <charrange><charclass>
        <charrange> ::= <ccchar> |
                        <ccchar> '-' <ccchar>
        <char> ::= <any character except metacharacters> |
                   '\' <any character at all>
        <ccchar> ::= <any character except '-' and ']'> |
                     '\' <any character at all>

        This means that parentheses have maximum precedence, followed
        by square brackets, followed by the closure operators,
        followed by concatenation, finally followed by alternation.
}

{turn this compiler define on to log the parsing progress and the
 final transition table; file is c:\regexparse.log}
{$DEFINE LogParse}

uses
  SysUtils,
  Classes,
  AAIntDeq,
  AAIntLst;

type
  TaaRegexParser = class
    private
      FRegexStr : string;
      FPosn     : PAnsiChar;
    protected
      procedure rpParseAtom;
      procedure rpParseCCChar;
      procedure rpParseChar;
      procedure rpParseCharClass;
      procedure rpParseCharRange;
      procedure rpParseExpr;
      procedure rpParseFactor;
      procedure rpParseTerm;
    public
      constructor Create(const aRegexStr : string);
      destructor Destroy; override;

      function Parse(var aErrorPos : integer) : boolean;
  end;

type
  PaaCharSet = ^TaaCharSet;
  TaaCharSet = set of char;

  TaaNFAMatchType = (  {types of matching performed...}
     mtNone,           {..no match (an epsilon no-cost move)}
     mtAnyChar,        {..any character}
     mtChar,           {..a particular character}
     mtClass,          {..a character class}
     mtNegClass,       {..a negated character class}
     mtTerminal,       {..the final state--no matching}
     mtUnused);        {..an unused state--no matching}

  TaaRegexError = (    {error codes for invalid regex strings}
     recNone,          {..no error}
     recSuddenEnd,     {..unexpected end of string}
     recMetaChar,      {..read metacharacter, but needed normal char}
     recNoCloseParen,  {..expected close paren, but not there}
     recExtraChars     {..not at end of string after parsing regex}
     );

  TaaUpcaseChar = function (aCh : char) : char;

  TaaRegexCompiler = class
    private
      FAnchorEnd  : boolean;
      FAnchorStart: boolean;
      FErrorCode  : TaaRegexError;
      FIgnoreCase : boolean;
      FPosn       : PAnsiChar;
      FRegexStr   : string;
      FStartState : integer;
      FTable      : TList;
      FUpcase     : TaaUpcaseChar;
      {$IFDEF LogParse}
      Log : System.Text;
      {$ENDIF}
    protected
      procedure rcSetIgnoreCase(aValue : boolean);
      procedure rcSetRegexStr(const aRegexStr : string);
      procedure rcSetUpcase(aValue : TaaUpcaseChar);

      procedure rcClear;
      procedure rcLevel1Optimize;
      procedure rcLevel2Optimize;
      function rcMatchSubString(const S   : string;
                                StartPosn : integer) : boolean;
      function rcAddState(aMatchType : TaaNFAMatchType;
                          aChar      : char;
                          aCharClass : PaaCharSet;
                          aNextState1: integer;
                          aNextState2: integer) : integer;
      function rcSetState(aState     : integer;
                          aNextState1: integer;
                          aNextState2: integer) : integer;

      function rcParseAnchorExpr : integer;
      function rcParseAtom : integer;
      function rcParseCCChar : char;
      function rcParseChar : integer;
      function rcParseCharClass(aClass : PaaCharSet) : boolean;
      function rcParseCharRange(aClass : PaaCharSet) : boolean;
      function rcParseExpr : integer;
      function rcParseFactor : integer;
      function rcParseTerm : integer;

      procedure rcWalkNoCostTree(aList  : TaaIntList;
                                 aState : integer);

      {$IFDEF LogParse}
      procedure rcDumpTable;
      {$ENDIF}
    public
      constructor Create(const aRegexStr : string);
      destructor Destroy; override;

      function Parse(var aErrorPos : integer;
                     var aErrorCode: TaaRegexError) : boolean;
      function MatchString(const S : string) : integer;


      property IgnoreCase : boolean
                  read FIgnoreCase write rcSetIgnoreCase;
      property RegexString : string
                  read FRegexStr write rcSetRegexStr;
      property Upcase : TaaUpcaseChar
                  read FUpcase write rcSetUpcase;
  end;

implementation

const
  MetaCharacters : set of char =
                   ['[', ']', '(', ')', '|', '*', '+', '?', '-', '.',
                    '^', '$'];
  {some handy constants}
  UnusedState = -1;
  NewFinalState = -2;
  CreateNewState = -3;
  ErrorState = -4;
  MustScan = -5;

type
  PaaNFAState = ^TaaNFAState;
  TaaNFAState = record
    sdNextState1: integer;
    sdNextState2: integer;
    sdNextList  : TaaIntList;
    sdClass     : PaaCharSet;
    sdMatchType : TaaNFAMatchType;
    sdChar      : char;
  end;


{===TaaRegexParser===================================================}
constructor TaaRegexParser.Create(const aRegexStr : string);
begin
  inherited Create;
  FRegexStr := aRegexStr;
end;
{--------}
destructor TaaRegexParser.Destroy;
begin
  inherited Destroy;
end;
{--------}
function TaaRegexParser.Parse(var aErrorPos : integer) : boolean;
begin
  Result := true;
  aErrorPos := 0;
  FPosn := PAnsiChar(FRegexStr);
  try
    rpParseExpr;
    if (FPosn^ <> #0) then begin
      Result := false;
      aErrorPos := FPosn - PAnsiChar(FRegexStr) + 1;
    end;
  except
    on E:Exception do begin
      Result := false;
      aErrorPos := FPosn - PAnsiChar(FRegexStr) + 1;
    end;
  end;
end;
{--------}
procedure TaaRegexParser.rpParseAtom;
begin
  case FPosn^ of
    '(' : begin
            inc(FPosn);
            writeln('open paren');
            rpParseExpr;
            if (FPosn^ <> ')') then
              raise Exception.Create('Regex error: expecting a closing parenthesis');
            inc(FPosn);
            writeln('close paren');
          end;
    '[' : begin
            inc(FPosn);
            if (FPosn^ = '^') then begin
              inc(FPosn);
              writeln('negated char class');
              rpParseCharClass;
            end
            else begin
              writeln('normal char class');
              rpParseCharClass;
            end;
            inc(FPosn);
          end;
    '.' : begin
            inc(FPosn);
            writeln('any character');
          end;
  else
    rpParseChar;
  end;{case}
end;
{--------}
procedure TaaRegexParser.rpParseCCChar;
begin
  if (FPosn^ = #0) then
    raise Exception.Create('Regex error: expecting a normal character, found null terminator');
  if FPosn^ in [']', '-'] then
    raise Exception.Create('Regex error: expecting a normal character, ie found a metacharacter');
  if (FPosn^ = '\') then begin
    inc(FPosn);
    writeln('escaped ccchar ', FPosn^);
    inc(FPosn);
  end
  else begin
    writeln('ccchar ', FPosn^);
    inc(FPosn);
  end;
end;
{--------}
procedure TaaRegexParser.rpParseChar;
begin
  if (FPosn^ = #0) then
    raise Exception.Create('Regex error: expecting a normal character, found null terminator');
  if FPosn^ in MetaCharacters then
    raise Exception.Create('Regex error: expecting a normal character, ie found a metacharacter');
  if (FPosn^ = '\') then begin
    inc(FPosn);
    writeln('escaped char ', FPosn^);
    inc(FPosn);
  end
  else begin
    writeln('char ', FPosn^);
    inc(FPosn);
  end;
end;
{--------}
procedure TaaRegexParser.rpParseCharClass;
begin
  rpParseCharRange;
  if (FPosn^ <> ']') then
    rpParseCharClass;
end;
{--------}
procedure TaaRegexParser.rpParseCharRange;
begin
  rpParseCCChar;
  if (FPosn^ = '-') then begin
    inc(FPosn);
    writeln('--range to--');
    rpParseCCChar;
  end;
end;
{--------}
procedure TaaRegexParser.rpParseExpr;
begin
  rpParseTerm;
  if (FPosn^ = '|') then begin
    inc(FPosn);
    writeln('alternation');
    rpParseExpr;
  end;
end;
{--------}
procedure TaaRegexParser.rpParseFactor;
begin
  rpParseAtom;
  case FPosn^ of
    '?' : begin
            inc(FPosn);
            writeln('zero or one');
          end;
    '*' : begin
            inc(FPosn);
            writeln('zero or more');
          end;
    '+' : begin
            inc(FPosn);
            writeln('one or more');
          end;
  end;{case}
end;
{--------}
procedure TaaRegexParser.rpParseTerm;
begin
  rpParseFactor;
  {Note: we have to "break the grammar" here. We've parsed a regular
         subexpression and we're possibly following on with another
         regular subexpression. There's no nice operator to key off
         for concatenation: we just have to know that for
         concatenating two subexpressions, the current character will
         be
           - an open parenthesis
           - an open square bracket
           - an any char operator
           - a character that's not a metacharacter
         i.e., the three possibilities for the start of an "atom" in
         our grammar}
  if (FPosn^ = '(') or
     (FPosn^ = '[') or
     (FPosn^ = '.') or
     ((FPosn^ <> #0) and not (FPosn^ in MetaCharacters)) then
    rpParseTerm;
end;
{====================================================================}


{===TaaRegexCompiler===================================================}
constructor TaaRegexCompiler.Create(const aRegexStr : string);
begin
  inherited Create;
  FRegexStr := aRegexStr;
  FIgnoreCase := true;
  FUpcase := System.Upcase;
  FTable := TList.Create;
  FTable.Capacity := 64;
end;
{--------}
destructor TaaRegexCompiler.Destroy;
begin
  if (FTable <> nil) then begin
    rcClear;
    FTable.Free;
  end;
  inherited Destroy;
end;
{--------}
function TaaRegexCompiler.MatchString(const S : string) : integer;
var
  i : integer;
  ErrorPos  : integer;
  ErrorCode : TaaRegexError;
begin
  {if the regex string hasn't been parsed yet, do so}
  if (FTable.Count = 0) then begin
    if not Parse(ErrorPos, ErrorCode) then begin
      raise Exception.Create(
         Format('The regex was invalid at position %d', [ErrorPos]));
    end;
  end;
  {now try and see if the string matches (empty strings don't)}
  Result := 0;
  if (S <> '') then
    {if the regex specified a start anchor, then we only need to check
     the string starting at the first position}
    if FAnchorStart then begin
      if rcMatchSubString(S, 1) then
        Result := 1;
    end
    {otherwise we try and match the string at every position and
     return at the first success}
    else begin
      for i := 1 to length(S) do
        if rcMatchSubString(S, i) then begin
          Result := i;
          Break;
        end;
    end;
end;
{--------}
function TaaRegexCompiler.Parse(var aErrorPos : integer;
                                var aErrorCode: TaaRegexError)
                                                            : boolean;
  {$IFDEF LogParse}
  procedure WriteError(aErrorPos : integer;
                       aErrorCode: TaaRegexError);
  begin
    writeln(Log, '***parse error found at ', aErrorPos);
    case aErrorCode of
      recNone         : writeln(Log, '-->no error');
      recSuddenEnd    : writeln(Log, '-->unexpected end of regex');
      recMetaChar     : writeln(Log, '-->found metacharacter in wrong place');
      recNoCloseParen : writeln(Log, '-->missing close paren');
      recExtraChars   : writeln(Log, '-->extra chars after valid regex');
    end;
    writeln(Log, '"', FRegexStr, '"');
    writeln(Log, '^':succ(aErrorPos));
  end;
  {$ENDIF}
begin
  {$IFDEF LogParse}
  System.Assign(Log, 'c:\regexparse.log');
  System.Rewrite(Log);
  try
    writeln(Log, 'Parsing regex: "', FRegexStr, '"');
  {$ENDIF}

  {clear the current transition table}
  rcClear;
  {empty regex strings are not allowed}
  if (FRegexStr = '') then begin
    Result := false;
    aErrorPos := 1;
    aErrorCode := recSuddenEnd;

    {$IFDEF LogParse}
    WriteError(aErrorPos, aErrorCode);
    {$ENDIF}

    Exit;
  end;
  {parse the regex string}
  FPosn := PAnsiChar(FRegexStr);
  FStartState := rcParseAnchorExpr;
  {if an error occurred or we're not at the end of the regex string,
   clear the transition table, return false and the error position}
  if (FStartState = ErrorState) or (FPosn^ <> #0) then begin
    if (FStartState <> ErrorState) and (FPosn^ <> #0) then
      FErrorCode := recExtraChars;
    rcClear;
    Result := false;
    aErrorPos := succ(FPosn - PAnsiChar(FRegexStr));
    aErrorCode := FErrorCode;

    {$IFDEF LogParse}
    WriteError(aErrorPos, aErrorCode);
    {$ENDIF}
  end
  {otherwise add a terminal state, optimize, return true}
  else begin
    rcAddState(mtTerminal, #0, nil, UnusedState, UnusedState);

    {$IFDEF LogParse}
    writeln(Log, 'Pre-level1 optimization...');
    rcDumpTable;
    {$ENDIF}

    rcLevel1Optimize;

    {$IFDEF LogParse}
    writeln(Log, 'Pre-level2 optimization...');
    rcDumpTable;
    {$ENDIF}

    rcLevel2Optimize;

    Result := true;
    aErrorPos := 0;
    aErrorCode := recNone;

    {$IFDEF LogParse}
    writeln(Log, 'Final table...');
    rcDumpTable;
    {$ENDIF}
  end;

  {$IFDEF LogParse}
  finally
    System.Close(Log);
  end;
  {$ENDIF}
end;
{--------}
function TaaRegexCompiler.rcAddState(aMatchType : TaaNFAMatchType;
                                     aChar      : char;
                                     aCharClass : PaaCharSet;
                                     aNextState1: integer;
                                     aNextState2: integer) : integer;
var
  StateData : PaaNFAState;
begin
  {create the new state record}
  StateData := AllocMem(sizeof(TaaNFAState));
  {set up the fields in the state record}
  if (aNextState1 = NewFinalState) then
    StateData^.sdNextState1 := succ(FTable.Count)
  else
    StateData^.sdNextState1 := aNextState1;
  StateData^.sdNextState2 := aNextState2;
  StateData^.sdMatchType := aMatchType;
  if (aMatchType = mtChar) then
    StateData^.sdChar := aChar
  else if (aMatchType = mtClass) or (aMatchType = mtNegClass) then
    StateData^.sdClass := aCharClass;
  {add the new state}
  Result := FTable.Count;
  FTable.Add(StateData);
end;
{--------}
procedure TaaRegexCompiler.rcClear;
var
  i : integer;
  StateData : PaaNFAState;
begin
  {free all items in the state transition table}
  for i := 0 to pred(FTable.Count) do begin
    StateData := PaaNFAState(FTable.List^[i]);
    if (StateData <> nil) then begin
      with StateData^ do begin
        if (sdMatchType = mtClass) or
           (sdMatchType = mtNegClass) then
          if (sdClass <> nil) then
            FreeMem(StateData^.sdClass);
        sdNextList.Free;
      end;
      Dispose(StateData);
    end;
  end;
  {clear the state transition table}
  FTable.Clear;
  FTable.Capacity := 64;
  FAnchorStart := false;
  FAnchorEnd := false;
end;
{--------}
{$IFDEF LogParse}
procedure TaaRegexCompiler.rcDumpTable;
var
  i, j : integer;
begin
  if (FTable.Count = 0) then
    writeln(Log, 'No transition table to dump!')
  else begin
    writeln(Log, 'Transition table dump for "', FRegexStr, '"');
    if FAnchorStart then
      writeln(Log, 'anchored at start of string');
    if FAnchorEnd then
      writeln(Log, 'anchored at end of string');
    writeln(Log, 'start state: ', FStartState:3);
    for i := 0 to pred(FTable.Count) do begin
      write(Log, i:3);
      with PaaNFAState(FTable[i])^ do begin
        case sdMatchType of
          mtNone    : write(Log, '  no match');
          mtAnyChar : write(Log, '  any char');
          mtChar    : write(Log, '    char:', sdChar);
          mtClass   : write(Log, '     class');
          mtNegClass: write(Log, ' neg class');
          mtTerminal: write(Log, '*******END');
          mtUnused  : write(Log, '        --');
        else
          write(Log, ' **error**');
        end;
        if (sdNextList <> nil) then begin
          write(Log, ' next:');
          for j := 0 to pred(sdNextList.Count) do
            write(Log, ' ', sdNextList[j]);
        end
        else begin
          if (sdMatchType <> mtTerminal) and
             (sdMatchType <> mtUnused) then begin
            write(Log, ' next1: ', sdNextState1:3);
            if (sdNextState2 <> UnusedState) then
              write(Log, ' next2: ', sdNextState2:3);
          end;
        end;
      end;
      writeln(Log);
    end;
  end;
  writeln(Log);
end;
{$ENDIF}
{--------}
procedure TaaRegexCompiler.rcLevel1Optimize;
var
  i : integer;
  Walker : PaaNFAState;
begin
  {level 1 optimization removes all states that have only a single
   no-cost move to another state}

  {cycle through all the state records, except for the last one}
  for i := 0 to (FTable.Count - 2) do begin
    {get this state}
    with PaaNFAState(FTable.List^[i])^ do begin
      {walk the chain pointed to by the first next state, unlinking
       the states that are simple single no-cost moves}
      Walker := PaaNFAState(FTable.List^[sdNextState1]);
      while (Walker^.sdMatchType = mtNone) and
            (Walker^.sdNextState2 = UnusedState) do begin
        sdNextState1 := Walker^.sdNextState1;
        Walker := PaaNFAState(FTable.List^[sdNextState1]);
      end;
      {walk the chain pointed to by the first next state, unlinking
       the states that are simple single no-cost moves}
      if (sdNextState2 <> UnusedState) then begin
        Walker := PaaNFAState(FTable.List^[sdNextState2]);
        while (Walker^.sdMatchType = mtNone) and
              (Walker^.sdNextState2 = UnusedState) do begin
          sdNextState2 := Walker^.sdNextState1;
          Walker := PaaNFAState(FTable.List^[sdNextState2]);
        end;
      end;
    end;
  end;
end;
{--------}
procedure TaaRegexCompiler.rcLevel2Optimize;
var
  i : integer;
begin
  {level 2 optimization removes all no-cost moves, except for those
   from the start state, if that is a no-cost move state}

  {cycle through all the state records, except for the last one}
  for i := 0 to (FTable.Count - 2) do begin
    {get this state}
    with PaaNFAState(FTable.List^[i])^ do begin
      {if it's not a no-cost move state or it's the start state...}
      if (sdMatchType <> mtNone) or (i = FStartState) then begin
        {create the state list}
        sdNextList := TaaIntList.Create;
        {walk the chain pointed to by the first next state, adding
         the non-no-cost states to the list}
        rcWalkNoCostTree(sdNextList, sdNextState1);
        {if this is the start state, and it's a no-cost move state
         walk the chain pointed to by the second next state, adding
         the non-no-cost states to the list}
        if (sdMatchType = mtNone) then
          rcWalkNoCostTree(sdNextList, sdNextState2);
      end;
    end;
  end;

  {cycle through all the state records, except for the last one,
   marking unused ones--not strictly necessary but good for debugging}
  for i := 0 to (FTable.Count - 2) do begin
    if (i <> FStartState) then
      with PaaNFAState(FTable.List^[i])^ do begin
        if (sdMatchType = mtNone) then
          sdMatchType := mtUnused;
      end;
  end;
end;
{--------}
function TaaRegexCompiler.rcMatchSubString(const S   : string;
                                           StartPosn : integer)
                                                            : boolean;
var
  i      : integer;
  Ch     : char;
  State  : integer;
  Deque  : TaaIntDeque;
  StrInx : integer;
begin
  {assume we fail to match}
  Result := false;
  {create the deque}
  Deque := TaaIntDeque.Create(64);
  try
    {enqueue the special value to start scanning}
    Deque.Enqueue(MustScan);
    {enqueue the first state}
    Deque.Enqueue(FStartState);
    {prepare the string index}
    StrInx := StartPosn - 1;
    Ch := #0; //just to fool the compiler
    {loop until the deque is empty or we run out of string}
    while (StrInx <= length(S)) and not Deque.IsEmpty do begin
      {pop the top state from the deque}
      State := Deque.Pop;
      {process the "must scan" state first}
      if (State = MustScan) then begin
        {if the deque is empty at this point, we might as well give up
         since there are no states left to process new characters}
        if not Deque.IsEmpty then begin
          {if we haven't run out of string, get the character, and
           enqueue the "must scan" state again}
          inc(StrInx);
          if (StrInx <= length(S)) then begin
            if IgnoreCase then
              Ch := Upcase(S[StrInx])
            else
              Ch := S[StrInx];
            Deque.Enqueue(MustScan);
          end;
        end;
      end
      {otherwise, process the state}
      else with PaaNFAState(FTable.List^[State])^ do begin
        case sdMatchType of
          mtNone :
            begin
              if (State <> FStartState) then
                Assert(false, 'no-cost states shouldn''t be seen');
              for i := 0 to pred(sdNextList.Count) do
                Deque.Push(sdNextList[i]);
            end;
          mtAnyChar :
            begin
              {for a match of any character, enqueue the next states}
              for i := 0 to pred(sdNextList.Count) do
                Deque.Enqueue(sdNextList[i]);
            end;
          mtChar :
            begin
              {for a match of a character, enqueue the next states}
              if (Ch = sdChar) then
                for i := 0 to pred(sdNextList.Count) do
                  Deque.Enqueue(sdNextList[i]);
            end;
          mtClass :
            begin
              {for a match within a class, enqueue the next states}
              if (Ch in sdClass^) then
                for i := 0 to pred(sdNextList.Count) do
                  Deque.Enqueue(sdNextList[i]);
            end;
          mtNegClass :
            begin
              {for a match not within a class, enqueue the next states}
              if not (Ch in sdClass^) then
                for i := 0 to pred(sdNextList.Count) do
                  Deque.Enqueue(sdNextList[i]);
            end;
          mtTerminal :
            begin
              {for a terminal state, the string successfully matched
               if the regex had no end anchor, or we're at the end
               of the string}
              if (not FAnchorEnd) or (StrInx > length(S)) then begin
                Result := true;
                Exit;
              end;
            end;
          mtUnused :
            begin
              Assert(false, 'unused states shouldn''t be seen');
            end;
        end;
      end;
    end;
    {if we reach this point we've either exhausted the deque or we've
     run out of string; if the former, the substring did not match
     since there are no more states. If the latter, we need to check
     the states left on the deque to see if one is the terminating
     state; if so the string matched the regular expression defined by
     the transition table}
    while not Deque.IsEmpty do begin
      State := Deque.Pop;
      with PaaNFAState(FTable.List^[State])^ do begin
        case sdMatchType of
          mtTerminal :
            begin
              {for a terminal state, the string successfully matched
               if the regex had no end anchor, or we're at the end
               of the string}
              if (not FAnchorEnd) or (StrInx > length(S)) then begin
                Result := true;
                Exit;
              end;
            end;
        end;{case}
      end;
    end;
  finally
    Deque.Free;
  end;
end;
{--------}
function TaaRegexCompiler.rcParseAnchorExpr : integer;
begin
  {check for an initial '^'}
  if (FPosn^ = '^') then begin
    FAnchorStart := true;
    inc(FPosn);

    {$IFDEF LogParse}
    writeln(Log, 'parsed start anchor');
    {$ENDIF}
  end;

  {parse an expression}
  Result := rcParseExpr;

  {if we were successful, check for the final '$'}
  if (Result <> ErrorState) then begin
    if (FPosn^ = '$') then begin
      FAnchorEnd := true;
      inc(FPosn);

      {$IFDEF LogParse}
      writeln(Log, 'parsed end anchor');
      {$ENDIF}
    end;
  end;
end;
{--------}
function TaaRegexCompiler.rcParseAtom : integer;
var
  MatchType : TaaNFAMatchType;
  CharClass : PaaCharSet;
begin
  case FPosn^ of
    '(' :
      begin
        {move past the open parenthesis}
        inc(FPosn);

        {$IFDEF LogParse}
        writeln(Log, 'parsed open paren');
        {$ENDIF}

        {parse a complete regex between the parentheses}
        Result := rcParseExpr;
        if (Result = ErrorState) then
          Exit;
        {if the current character is not a close parenthesis,
         there's an error}
        if (FPosn^ <> ')') then begin
          FErrorCode := recNoCloseParen;
          Result := ErrorState;
          Exit;
        end;
        {move past the close parenthesis}
        inc(FPosn);

        {$IFDEF LogParse}
        writeln(Log, 'parsed close paren');
        {$ENDIF}
      end;
    '[' :
      begin
        {move past the open square bracket}
        inc(FPosn);

        {$IFDEF LogParse}
        writeln(Log, 'parsed open square bracket (start of class)');
        {$ENDIF}

        {if the first character in the class is a '^' then the
         class if negated, otherwise it's a normal one}
        if (FPosn^ = '^') then begin
          inc(FPosn);
          MatchType := mtNegClass;

          {$IFDEF LogParse}
          writeln(Log, 'it is a negated class');
          {$ENDIF}
        end
        else begin
          MatchType := mtClass;

          {$IFDEF LogParse}
          writeln(Log, 'it is a normal class');
          {$ENDIF}
        end;
        {allocate the class character set and parse the character
         class; this will return either with an error, or when the
         closing square bracket is encountered}
        New(CharClass);
        CharClass^ := [];
        if not rcParseCharClass(CharClass) then begin
          Dispose(CharClass);
          Result := ErrorState;
          Exit;
        end;
        {move past the closing square bracket}
        Assert(FPosn^ = ']',
               'the rcParseCharClass terminated without finding a "]"');
        inc(FPosn);

        {$IFDEF LogParse}
        writeln(Log, 'parsed close square bracket (end of class)');
        {$ENDIF}

        {add a new state for the character class}
        Result := rcAddState(MatchType, #0, CharClass,
                             NewFinalState, UnusedState);
      end;
    '.' :
      begin
        {move past the period metacharacter}
        inc(FPosn);

        {$IFDEF LogParse}
        writeln(Log, 'parsed anychar operator "."');
        {$ENDIF}

        {add a new state for the 'any character' token}
        Result := rcAddState(mtAnyChar, #0, nil,
                             NewFinalState, UnusedState);
      end;
  else
    {otherwise parse a single character}
    Result := rcParseChar;
  end;{case}
end;
{--------}
function TaaRegexCompiler.rcParseCCChar : char;
begin
  {if we hit the end of the string, it's an error}
  if (FPosn^ = #0) then begin
    FErrorCode := recSuddenEnd;
    Result := #0;
    Exit;
  end;
  {if the current char is a metacharacter (at least in terms of a
   character class), it's an error}
  if FPosn^ in [']', '-'] then begin
    FErrorCode := recMetaChar;
    Result := #0;
    Exit;
  end;
  {otherwise return the character and advance past it}
  if (FPosn^ = '\') then
    {..it's an escaped character: get the next character instead}
    inc(FPosn);
  Result := FPosn^;
  inc(FPosn);

  {$IFDEF LogParse}
  writeln(Log, 'parsed charclass char: "', Result, '"');
  {$ENDIF}
end;
{--------}
function TaaRegexCompiler.rcParseChar : integer;
var
  Ch : char;
begin
  {if we hit the end of the string, it's an error}
  if (FPosn^ = #0) then begin
    Result := ErrorState;
    FErrorCode := recSuddenEnd;
    Exit;
  end;
  {if the current char is one of the metacharacters, it's an error}
  if FPosn^ in MetaCharacters then begin
    Result := ErrorState;
    FErrorCode := recMetaChar;
    Exit;
  end;
  {otherwise add a state for the character}
  {..if it's an escaped character: get the next character instead}
  if (FPosn^ = '\') then
    inc(FPosn);
  if IgnoreCase then
    Ch := Upcase(FPosn^)
  else
    Ch := FPosn^;
  Result := rcAddState(mtChar, Ch, nil, NewFinalState, UnusedState);
  inc(FPosn);

  {$IFDEF LogParse}
  writeln(Log, 'parsed char: "', Ch, '"');
  {$ENDIF}
end;
{--------}
function TaaRegexCompiler.rcParseCharClass(aClass : PaaCharSet) : boolean;
begin
  {assume we can't parse a character class properly}
  Result := false;
  {parse a character range; if we can't there was an error and the
   caller will take care of it}
  if not rcParseCharRange(aClass) then
    Exit;
  {if the current character was not the right bracket, parse another
   character class (note: we're removing the tail recursion here)}
  while (FPosn^ <> ']') do begin
    if not rcParseCharRange(aClass) then
      Exit;
  end;
  {if we reach here we were successful}
  Result := true;
end;
{--------}
function TaaRegexCompiler.rcParseCharRange(aClass : PaaCharSet) : boolean;
var
  StartChar : char;
  EndChar   : char;
  Ch        : char;
begin
  {assume we can't parse a character range properly}
  Result := false;
  {parse a single character; if it's null there was an error}
  StartChar := rcParseCCChar;
  if (StartChar = #0) then
    Exit;
  {if the current character is not a dash, the range consisted of a
   single character}
  if (FPosn^ <> '-') then begin
    if IgnoreCase then
      Include(aClass^, Upcase(StartChar))
    else
      Include(aClass^, StartChar)
  end
  {otherwise it's a real range, so get the character at the end of the
   range; if that's null, there was an error}
  else begin

    {$IFDEF LogParse}
    writeln(Log, '-range to-');
    {$ENDIF}

    inc(FPosn); {move past the '-'}
    EndChar := rcParseCCChar;
    if (EndChar = #0) then
      Exit;
    {build the range as a character set}
    if (StartChar > EndChar) then begin
      Ch := StartChar;
      StartChar := EndChar;
      EndChar := Ch;
    end;
    for Ch := StartChar to EndChar do begin
      Include(aClass^, Ch);
      if IgnoreCase then
        Include(aClass^, Upcase(Ch));
    end;
  end;
  {if we reach here we were successful}
  Result := true;
end;
{--------}
function TaaRegexCompiler.rcParseExpr : integer;
var
  StartState1 : integer;
  StartState2 : integer;
  EndState1   : integer;
  OverallStartState : integer;
begin
  {assume the worst}
  Result := ErrorState;
  {parse an initial term}
  StartState1 := rcParseTerm;
  if (StartState1 = ErrorState) then
    Exit;
  {if the current character is *not* a pipe character, no alternation
   is present so return the start state of the initial term as our
   start state}
  if (FPosn^ <> '|') then
    Result := StartState1
  {otherwise, we need to parse another expr and join the two together
   in the transition table}
  else begin

    {$IFDEF LogParse}
    writeln(Log, 'OR (alternation)');
    {$ENDIF}

    {advance past the pipe}
    inc(FPosn);
    {the initial term's end state does not exist yet (although there
     is a state in the term that points to it), so create it}
    EndState1 := rcAddState(mtNone, #0, nil, UnusedState, UnusedState);
    {for the OR construction we need a new initial state: it will
     point to the initial term and the second just-about-to-be-parsed
     expr}
    OverallStartState := rcAddState(mtNone, #0, nil,
                                    UnusedState, UnusedState);
    {parse another expr}
    StartState2 := rcParseExpr;
    if (StartState2 = ErrorState) then
      Exit;
    {alter the state state for the overall expr so that the second
     link points to the start of the second expr}
    Result := rcSetState(OverallStartState, StartState1, StartState2);
    {now set the end state for the initial term to point to the final
     end state for the second expr and the overall expr}
    rcSetState(EndState1, FTable.Count, UnusedState);
  end;
end;
{--------}
function TaaRegexCompiler.rcParseFactor : integer;
var
  StartStateAtom : integer;
  EndStateAtom   : integer;
begin
  {assume the worst}
  Result := ErrorState;
  {first parse an atom}
  StartStateAtom := rcParseAtom;
  if (StartStateAtom = ErrorState) then
    Exit;
  {check for a closure operator}
  case FPosn^ of
    '?' : begin
            {$IFDEF LogParse}
            writeln(Log, 'zero or one closure');
            {$ENDIF}

            {move past the ? operator}
            inc(FPosn);
            {the atom's end state doesn't exist yet, so create one}
            EndStateAtom := rcAddState(mtNone, #0, nil,
                                       UnusedState, UnusedState);
            {create a new start state for the overall regex}
            Result := rcAddState(mtNone, #0, nil,
                                 StartStateAtom, EndStateAtom);
            {make sure the new end state points to the next unused
             state}
            rcSetState(EndStateAtom, FTable.Count, UnusedState);
          end;
    '*' : begin
            {$IFDEF LogParse}
            writeln(Log, 'zero or more closure');
            {$ENDIF}

            {move past the * operator}
            inc(FPosn);
            {the atom's end state doesn't exist yet, so create one;
             it'll be the start of the overall regex subexpression}
            Result := rcAddState(mtNone, #0, nil,
                                 NewFinalState, StartStateAtom);
          end;
    '+' : begin
            {$IFDEF LogParse}
            writeln(Log, 'one or more closure');
            {$ENDIF}

            {move past the + operator}
            inc(FPosn);
            {the atom's end state doesn't exist yet, so create one}
            rcAddState(mtNone, #0, nil, NewFinalState, StartStateAtom);
            {the start of the overall regex subexpression will be the
             atom's start state}
            Result := StartStateAtom;
          end;
  else
    Result := StartStateAtom;
  end;{case}
end;
{--------}
function TaaRegexCompiler.rcParseTerm : integer;
var
  StartState2 : integer;
  EndState1   : integer;
begin
  {parse an initial factor, the state number returned will also be our
   return state number}
  Result := rcParseFactor;
  if (Result = ErrorState) then
    Exit;
  {Note: we have to "break the grammar" here. We've parsed a regular
         subexpression and we're possibly following on with another
         regular subexpression. There's no nice operator to key off
         for concatenation: we just have to know that for
         concatenating two subexpressions, the current character will
         be
           - an open parenthesis
           - an open square bracket
           - an any char operator
           - a character that's not a metacharacter
         i.e., the three possibilities for the start of an "atom" in
         our grammar}
  if (FPosn^ = '(') or
     (FPosn^ = '[') or
     (FPosn^ = '.') or
     ((FPosn^ <> #0) and not (FPosn^ in MetaCharacters)) then begin
    {$IFDEF LogParse}
    writeln(Log, 'concatenation');
    {$ENDIF}

    {the initial factor's end state does not exist yet (although there
     is a state in the term that points to it), so create it}
    EndState1 := rcAddState(mtNone, #0, nil, UnusedState, UnusedState);
    {parse another term}
    StartState2 := rcParseTerm;
    if (StartState2 = ErrorState) then begin
      Result := ErrorState;
      Exit;
    end;
    {join the first factor to the second term}
    rcSetState(EndState1, StartState2, UnusedState);
  end;
end;
{--------}
procedure TaaRegexCompiler.rcSetIgnoreCase(aValue : boolean);
begin
  if (aValue <> FIgnoreCase) then begin
    rcClear;
    FIgnoreCase := aValue;
  end;
end;
{--------}
procedure TaaRegexCompiler.rcSetRegexStr(const aRegexStr : string);
begin
  if (aRegexStr <> FRegexStr) then begin
    rcClear;
    FRegexStr := aRegexStr;
  end;
end;
{--------}
function TaaRegexCompiler.rcSetState(aState     : integer;
                                     aNextState1: integer;
                                     aNextState2: integer) : integer;
var
  StateData : PaaNFAState;
begin
  Assert((0 <= aState) and (aState < FTable.Count),
         'trying to change an invalid state');

  {get the state record and change the transition information}
  StateData := PaaNFAState(FTable.List^[aState]);
  StateData^.sdNextState1 := aNextState1;
  StateData^.sdNextState2 := aNextState2;
  Result := aState;
end;
{--------}
procedure TaaRegexCompiler.rcSetUpcase(aValue : TaaUpcaseChar);
begin
  if not Assigned(aValue) then
    FUpcase := System.Upcase
  else
    FUpcase := aValue;
end;
{--------}
procedure TaaRegexCompiler.rcWalkNoCostTree(aList  : TaaIntList;
                                            aState : integer);
begin
  {look at this state's record...}
  with PaaNFAState(FTable.List^[aState])^ do begin
    {if it's a no-cost state, recursively walk the
     first, then the second chain}
    if (sdMatchType = mtNone) then begin
      rcWalkNoCostTree(aList, sdNextState1);
      rcWalkNoCostTree(aList, sdNextState2);
    end
    {otherwise, add it to the list}
    else
      aList.Add(aState);
  end;
end;
{====================================================================}

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end.