part1-introduction.pas

{--------------------------------------------------------------}
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.
{--------------------------------------------------------------}