Давайте создадим компилятор!   ::   Креншоу Джек

Никаких других специальных методов не требуется… каждый удачный вызов GetChar считывает следующий символ из потока.



{–}

program Cradle;

{–}

{ Constant Declarations }

const TAB = ^I;

{–}

{ Variable Declarations }

var Look: char; { Lookahead Character }

{–}

{ Read New Character From Input Stream }

procedure GetChar;

begin

Read(Look);

end;

{–}

{ Report an Error }

procedure Error(s: string);

begin

WriteLn;

WriteLn(^G, 'Error: ', s, '.');

end;

{–}

{ Report Error and Halt }

procedure Abort(s: string);

begin

Error(s);

Halt;

end;

{–}

{ Report What Was Expected }

procedure Expected(s: string);

begin

Abort(s + ' Expected');

end;

{–}

{ Match a Specific Input Character }

procedure Match(x: char);

begin

if Look = x then GetChar

else Expected('''' + x + '''');

end;

{–}

{ Recognize an Alpha Character }

function IsAlpha(c: char): boolean;

begin

IsAlpha := upcase(c) in ['A'..'Z'];

end;

{–}

{ Recognize a Decimal Digit }

function IsDigit(c: char): boolean;

begin

IsDigit := c in ['0'..'9'];

end;

{–}

{ Get an Identifier }

function GetName: char;

begin

if not IsAlpha(Look) then Expected('Name');

GetName := UpCase(Look);

GetChar;

end;

{–}

{ Get a Number }

function GetNum: char;

begin

if not IsDigit(Look) then Expected('Integer');

GetNum := Look;

GetChar;

end;

{–}

{ Output a String with Tab }

procedure Emit(s: string);

begin

Write(TAB, s);

end;

{–}

{ Output a String with Tab and CRLF }

procedure EmitLn(s: string);

begin

Emit(s);

WriteLn;

end;

{–}

{ Initialize }

procedure Init;

begin

GetChar;

end;

{–}

{ Main Program }

begin

Init;

end.