Re: Error reporting in LR parsers

In <1989Aug6.024931.10014@esegue.uucp>, Dave Jones gives a rebuttal stating
how a default reduction in yacc has eliminated acceptable tokens from the
token list when an error occurs. The problem can be solved by generating
the list of acceptable tokens *before* returning the error token. This
method requires that you test the tokens before returning them to yacc (in
the scanner).


In the case given 'i = j k', the scanner upon reading 'k' checks the parser
state to see whether an identifier is acceptable in this state. This will
be the state prior to the default reduction, where + and * are still
acceptable. The list of acceptable tokens is remembered and the erroneous
token is returned. The 'yyerror' function then prints out the (perhaps
decoded) list of acceptable tokens.
--
          David Lai (lai@mips.com || {ames,prls,pyramid,decwrl}!mips!lai)

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