shift_stmt_expr grammar question

shift_stmt_expr grammar question

[Jeremy Sowden]

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Just noticed that the production for right shifts differs from the
production for left shifts (src/parser_bison.y, ll. 3020ff.):

  shift_stmt_expr    :       primary_stmt_expr
                     |       shift_stmt_expr         LSHIFT          primary_stmt_expr
                     {
                             $$ = binop_expr_alloc(&@$, OP_LSHIFT, $1, $3);
                     }
                     |       shift_stmt_expr         RSHIFT          primary_rhs_expr
                     {
                             $$ = binop_expr_alloc(&@$, OP_RSHIFT, $1, $3);
                     }
                     ;

Is there a reason why the RHS of LSHIFT is primary_stmt_expr, but the
RHS of RSHIFT is primary_rhs_expr?

J.

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Re: shift_stmt_expr grammar question

[Pablo Neira Ayuso]

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Hi Jeremy,

On Sun, Mar 08, 2020 at 10:40:03AM +0000, Jeremy Sowden wrote:
> Just noticed that the production for right shifts differs from the
> production for left shifts (src/parser_bison.y, ll. 3020ff.):
> 
>   shift_stmt_expr    :       primary_stmt_expr
>                      |       shift_stmt_expr         LSHIFT          primary_stmt_expr
>                      {
>                              $$ = binop_expr_alloc(&@$, OP_LSHIFT, $1, $3);
>                      }
>                      |       shift_stmt_expr         RSHIFT          primary_rhs_expr
>                      {
>                              $$ = binop_expr_alloc(&@$, OP_RSHIFT, $1, $3);
>                      }
>                      ;
> 
> Is there a reason why the RHS of LSHIFT is primary_stmt_expr, but the
> RHS of RSHIFT is primary_rhs_expr?

It's likely a leftover. The rhs rule was introduced to reduce chances
of hitting shift/reduce conflicts, and to restrict syntax on the rhs.

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