ISO Pascal reference manual

*ERROR 21 -- has been used in its own definition
This error is caused by attempting to use < name > to define itself. Note
that the definition of a record may include a pointer to a record of its own
type.
PROGRAM fail;
CONST fool = -fool; [???]
TYPE t = ARRAY [1..5] OF t; I???)
BEGIN
END.
*ERROR 22 -- has already been defined
This error is caused by attempting to define a procedure or function more
than once in the same block.
PROGRAM fail(output);
PROCEDURE fred; BEGIN
writelm('fred 1');
END;
PROCEDURE fred; BEGIN
writeln('fred 2');
END;
BEGIN
fred;
END.
*ERROR 23 -- has not been declared
< name > has been used either before it has been declared or without any
declaration.
PROGRAM fail;
VAR j : integer;
BEGIN
j := k; [k is unknown)
END.
52 Pascal Issue I