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getting shift/reduce errors in my grammar


getting shift/reduce errors in my grammar

By : Manoranjan Kumar
Date : November 14 2020, 04:51 PM
Hope that helps Your key_spec rule is malformed. Indeed you have an infinite recursion.
You should change it for something like
code :
key_spec: /* Empty. */
    | key_spec key_spec_content
;


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Bison grammar (1 reduce/reduce 1 shift/reduce )

Bison grammar (1 reduce/reduce 1 shift/reduce )


By : demozylak
Date : March 29 2020, 07:55 AM
will be helpful for those in need Your grammar is ambiguous. An A can be an Aexp or an Rexp. But an Rexp can also be an Aexp. This leads to a reduce/reduce conflict.
Let's say you give your parser this token sequence as input:
How do I fix this shift-reduce conflict in my PLY grammar?

How do I fix this shift-reduce conflict in my PLY grammar?


By : Songkran Somana
Date : March 29 2020, 07:55 AM
hop of those help? If this is the set of items that form a "state" of the parser, then you haven't written it down right:
code :
fn_call -> ID . L_PAREN fn_args R_PAREN
assignment -> ID . ASSIGN value
assignment -> ID . ASSIGN container
value -> ID .  *missing lookahead set*
 value -> ID
Not sure if this LR(1) grammar has shift/reduce conflict

Not sure if this LR(1) grammar has shift/reduce conflict


By : user3305926
Date : March 29 2020, 07:55 AM
it helps some times You need to check shift-reduce(SR) or reduce-reduce(RR) problem
In state 4 which yo have mentioned there is only one reduce entry S-> AA., $ therefore there is no RR problem. Check for SR :
Solving reduce/reduce and shift/reduce conflicts in bison grammar

Solving reduce/reduce and shift/reduce conflicts in bison grammar


By : Nicole
Date : March 29 2020, 07:55 AM
Hope that helps This response is to your UPDATE section, since that's kind of the heart of the problem.
The TL;DR answer is that the precedence-and-associativity declarations %left '+' and %left '*' apply while parsing BINOP but not while parsing expr, so they're too early (they do nothing at this point) and are gone by the time they are needed.
code :
$ cat expr.y
%token TOK_INTCON
%left '+'
%left '*'

%%
expr : expr BINOP expr
     | TOK_INTCON 

BINOP :  '+'  
      |  '*'
%%
$ bison -v expr.y
expr.y: warning: 2 shift/reduce conflicts [-Wconflicts-sr]
1 op 2 op 3
  op
 /  \
1    op
    /  \
   2    3
    op
   /  \
  op    3
 /  \
1    2
$ cat expr-repaired.y
%token TOK_INTCON
%left '+'
%left '*'

%%
expr : expr '+' expr
     | expr '*' expr
     | TOK_INTCON 
%%
$ bison -v expr-repaired.y
$ 
State 6

    1 expr: expr . '+' expr
    1     | expr '+' expr .
    2     | expr . '*' expr

    '*'  shift, and go to state 5

    $default  reduce using rule 1 (expr)
Converting Extended BNF to Bison grammar, but having shift/reduce errors

Converting Extended BNF to Bison grammar, but having shift/reduce errors


By : tim
Date : March 29 2020, 07:55 AM
wish helps you The conflict basically results from the nullability of contentseq. That forces the parser to recognise an empty contentseq before it recognises a longer contentseq. And that produces a conflict when the input starts BEGINDOCUMENT WHITESPACE, because at the point before the WHITESPACE, it is not knowable whether that empty contentseq should be reduced.
You can easily resolve that by making contentseq non-nullable (contentseq: content | contentseq content), at the cost of having to explicitly handle omitted sequences:
code :
documentbody: %empty | contentseq | maketitle optionalcs
contentseq: content | contentseq content
optionalcs: %empty | contentseq
maketitle: WHITESPACE MAKETITLE | MAKETITLE
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