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Selasa, 31 Mei 2011

[kuliah] listing praktikum



unit Scanner;

interface

uses winCRT;
const
ALNG = 30; {Number of significant chars in identifiers.}
eof = #26;
tab = #009;
LineFeed = #010;
space = #032;
car_return = #013;

type
Alfa = string [ALNG];

{Recognized symbol tokens.}
tokens = (
t_int, t_add, t_sub, t_mul, t_rdiv, t_double_mul,
t_assign { ':=' },
t_lbrack { '[' }, t_rbrack { ']' },
t_lparent { '(' }, t_rparent { ')' },
t_id, t_else, t_if, t_then
);

const
num_reserved_word = 3; {number of reserved word.}

{recognized reserved word strings.}
KeyStr : array [1..num_reserved_word] of Alfa = (
'else', 'if', 'then'
);

{Recognized reserved word tokens}
KeySym : array [1..num_reserved_word] of tokens = (
t_else, t_if, t_then
);

var
FIn : string[12]; {input file name}
FInput : text; {Input file pointer}

LookAhead : boolean; {TRUE if had been read ahead, else FALSE}
Enum : boolean; {TRUE if an enumeration delimeter countered}
Ch : char; {Read from finput}
token : tokens; {current token}
Id : Alfa; {current identifier}
Inum : longint; {integer number read, must be in --> integer;}
LineNumber : integer;

procedure initialize; {membuka file}
procedure scan;
procedure terminate; {menutup file}

implementation

procedure Initialize;
{Initialize variables}
begin
if (ParamCount < 1)
then repeat
Write ('File Sumber (.pas) : ');
ReadLn (FIn);
until (Length(FIn) <> 0)
else FIn := ParamStr (1);
if (Pos('.', FIn) = 0)
then FIn := FIn + '.pas';
{$I-}
Assign(FInput, FIn);
Reset(FInput);
{$I+}
if (IOResult <> 0)
then begin
WriteLn('Tidak bisa mengakses file: ''', FIn, '''');
Halt;
end;

FIn := Copy(FIn, 1, Pos('.', FIn) - 1) + '.out';

LookAhead := FALSE;
Enum := FALSE;
Ch := ' ';
LineNumber := 1;
End;

procedure Terminate;
begin
close(FInput);
end;

procedure GetCh;
{get a charakter from finput}
begin
Read(FInput, Ch);
end;

procedure error_report(id : byte);
begin
case id of
1 : writeln('Error --> unknown charakter ''', Ch, ''' Line : ', LineNumber);
2 : writeln('Error --> comment not limited Line' , LineNumber);
3 : writeln('Error -->integer overflow Line',LineNumber);
end;
end;

procedure Scan;
{Scan input text, and send a token}
var
Idx : integer;
e : integer;
begin
if (not LookAhead)
then GetCh;
LookAhead := FALSE;
repeat
case ch of
tab,LineFeed, space : GetCh;
car_return :
begin
GetCh;
inc (LineNumber);
end;
eof : {end of file}
Exit;
'A'..'Z', 'a'..'z' : {identifier}
begin
Id := '';
repeat
Id := Id + Ch;
GetCh;
until (not (Ch in['0'..'9', 'A'..'Z', 'a'..'z']));
LookAhead :=TRUE;
Idx := 0;
repeat
Idx := Idx + 1;
until ( (Idx = num_reserved_word) or (Id = KeyStr[Idx]));
if (Id = KeyStr[Idx])
then token := KeySym[Idx]
else token := t_id;
exit;
end;
'0'..'9' : {number}
begin
Inum := 0;
token := t_int;
repeat
Inum := Inum * 10 + (ord(Ch) - ord('0'));
GetCh;
until (not (Ch in['0'..'9']));
LookAhead := true;
Exit;
end;
'+' :
begin
token := t_add;
exit ;
end;
'-' :
begin
token := t_sub;
exit;
end;
'*' :
begin
getch;
if (ch = '*')
then token := t_double_mul
else begin
token := t_mul;
lookAhead := true;
end;
exit;
end;
'/' :
begin
token := t_rdiv;
exit;
end;
')' :
begin
token := t_rparent;
exit;
end;
'[' :
begin
token := t_lbrack;
exit;
end;
']' :
begin
token := t_rbrack;
exit;
end;
':' :
begin
GetCh;
if (Ch = '=')
then begin
token := t_assign;
end
else begin
WriteLn('Error --> unknown character ":" Line : ', LineNumber);
lookahead := true;
end;
Exit;
end;
'(' :
begin
GetCh;
if (Ch <> '*')
then begin
token := t_lparent;
LookAhead := TRUE;
Exit;
end
else begin
GetCh;
if (Ch = eof)
then begin
error_report (2);
exit;
end;
repeat
while (Ch <> '*')
do begin
GetCh;
if (Ch = eof) then
begin
error_report (2);
Exit;
end;
end;
GetCh;
if (Ch = eof)
then begin
error_report (2);
Exit;
end;
until (Ch = ')');
GetCh;
end;
end;
else
begin
error_report(1);
GetCh;
end;
end; {case}
until FALSE;
end;

end.

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