UCS: Isolated scanner

UCS: Isolated scanner
-------------


Usually, in classical compilers with recursive parsing, a lexical
scanner is called from different places of the parser. For example,
something like :


procedure expression;
procedure term;
procedure factor;
begin
if symbol = leftSy {"("}
then
begin
getSymbol (symbol);
expression;
end
else...........
end; {factor}


begin {term}
factor;
while symbol = mulSy {"*"} do
begin
getSymbol (symbol);
factor;
.................................


In contrast, in the MT2 Universal Compiler Shell (MT2UCS; please,
see <http://www.glasnet.ru/~mtrofimov/> for more info ...) I
implemented "an isolated scanner":


procedure compile;


  begin
    while not eof do
            begin
             getSymbol (symbol); {only one call here}
                  if testError then exit (compile);
                  parse (symbol); {there is no call of getSymbol in the parser}
            end;
  end; {compile}


This architecture looks like much more suitable for lexical errors
handing, for debugging and for optimization.


What do you think about? Do you know another examples of similar
architecture?


Thanks,
________________________________________________________________
Michael I. Trofimov
Russian Academy of Sci. Moscow, Russia
email: mtrofimov@glas.apc.org
http://www.glasnet.ru/~mtrofimov/
--

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