problems with absolute value structure in algebraic grammar

[Samad Lotia]

Here is my grammar from y.output:

   0  $accept : statement_list $end

   1  $$1 :

   2  statement_list : statement_list statement $$1
terminal
   3                 |
   4                 | statement_list error terminal
   5                 | terminal

   6  terminal : TERMINAL
   7           | EOL_TERMINAL

   8  statement : enclosed_statements
   9            | statement '+' statement
  10            | statement '-' statement
  11            | statement '*' statement
  12            | statement '/' statement
  13            | statement '%' statement
  14            | '-' statement
  15            | SYMBOL '=' statement

  16  enclosed_statements : enclosed_statement
  17                      | enclosed_statements
enclosed_statement

  18  enclosed_statement : VALUE
  19                     | SYMBOL
  20                     | enclosed_statement '^'
enclosed_statement
  21                     | '(' statement ')'
  22                     | '|' statement '|'
  23                     | FUNC_NAME '(' param_list
')'

  24  param_list :
  25             | polyparams

  26  polyparams : statement
  27             | polyparams ',' statement

The purpose of this grammar file is to produce a
parser which can parse algebraic expressions. The
purpose of the enclosed_statements rule is to support
implicit multiplication. For example, the expression:

9acos(0.5)

Really means:

9*acos(0.5)

Or the expression:

8|-2|(2^3)

Really means:

8*abs(-2)*(2^3)


When bison parses this grammar file, it reports a
shift/reduce conflict at line 22. It, for some reason,
cannot accept rules like this:
enclosed_statement: (a_token) statement (same_token)
For example, if I change line 21 from

enclosed_statement :
  21                     | '(' statement ')'

To:

enclosed_statement :
  21                     | '(' statement '('

This also produces a shift/reduce conflict. However,
if I change the left-hand side from
"enclosed_statement" to "statement," there is no
shift/reduce conflict. For example:

statement:               '|' statement '|'

Is accepted and works but:

enclosed_statement:      '|' statement '|'

does not work.
How can I solve this shift/reduce conflict?

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