Category : Pascal Source Code
Archive   : LEX_YACC.ZIP
Filename : TABLE.L

{ TABLE.L: Lex demonstration program for the use of character tables;
accepts identifiers, signed integers, whitespace and newline as input
and prints out the names of the matched tokens; unrecognized characters
are converted to and echoed as '?' (ASCII 63). }

uses LexLib;

{ redefined input functions that remap characters: }
function input : char; forward;
procedure unput(c : char); forward;

%T
1 Aa
2 Bb
3 Cc
{ ... }
26 Zz
27 \ \t
28 +
29 -
30 0
31 1
{ ... }
39 9
40 \n
%T

letter [A-Z]
digit [0-9]

%%

{letter}({letter}|{digit})* write(' ');
[+-]?{digit}+ write(' ');
" "+ write(' ');
\n writeln('');
. write(yytext[1]);

%%

(* implementation of input functions and main program: *)

var buf : string; (* lookahead buffer *)
function input : char;
var c : char;
begin
if length(buf)>0 then
(* get char from lookahead buffer: *)
begin
input := buf[1];
delete(buf, 1, 1)
end
else
begin
(* get character from input file (converting line end
to newline, and handling end of file): *)
if eof(yyin) then
c := #0
else if eoln(yyin) then
begin
c := #10; (* newline *)
readln(yyin)
end
else
read(yyin, c);
(* remap characters: *)
case c of
#0: input := #0;
'a'..'z': input := chr(succ(ord(c)-ord('a')));
'A'..'Z': input := chr(succ(ord(c)-ord('A')));
' ', #9: input := #27;
'+': input := #28;
'-': input := #29;
'0'..'9': input := chr(ord(c)-ord('0')+30);
#10: input := #40;
else input := '?'; (* denotes illegal character *)
end;
end
end(*input*);
procedure unput(c : char);
begin
buf := c+buf
end(*unput*);

begin
buf := '';
if yylex=0 then (* done *)
end.