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Re: How to change default outcome of shift/reduce conflict?


From: Anthony DeRobertis
Subject: Re: How to change default outcome of shift/reduce conflict?
Date: Sat, 12 Jan 2002 03:53:30 -0500

Hans Aberg writes:
You can use the Bison %left command on your "or" operator (see the manual
for calculator example).

OR is already %left. The actual lines look like this:
answer_statement: ANSWER expr answer_btn_list   { ... }
                | ANSWER_FILE                   { ... }
                | ANSWER_FILE expr              { ... }
                | ANSWER_FILE expr OF TYPE expr { ... }
;
answer_btn_list: WITH answer_btn_list_oneplus   { ... }
               | { ... }
               ;
answer_btn_list_oneplus: answer_btn_list_oneplus OR expr        { ... }
                       | expr                                   { ... }
;
Now, expr contains, among many other lines,
expr: ...
  | expr OR expr        { ... }
    ...
; The problem is a line which looks like this
ANSWER expr WITH expr OR expr
^^ Bison chooses the resolve the ambiguous grammar by shifting at the

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