+** Use syntax_error from the scanner?
+This would provide a means to raise syntax error from function called
+from the scanner. Actually, there is no good solution to report a
+lexical error in general. Usually they are kept at the scanner level
+only, ignoring the guilty token. But that might not be the best bet,
+since we don't benefit from the syntactic error recovery.
+
+We still have the possibility to return an invalid token number, which
+does the trick. But then the error message from the parser is poor
+(something like "unexpected $undefined"). Since the scanner probably
+already reported the error, we should directly enter error-recovery,
+without reporting the error message (i.e., YYERROR's semantics).
+
+Back to lalr1.cc (whose name is now quite unfortunate, since it also
+covers lr and ielr), if we support exceptions from yylex, should we
+propose a lexical_error in addition to syntax_error? Should they have
+a common root, say parse_error? Should syntax_error be renamed
+syntactic_error for consistency with lexical_error?
+
+** Variable names.
+What should we name `variant' and `lex_symbol'?
+