Below is a BNF description of the constants of the Logix languages.

<constant> ::= <string>
               <number>
               []

<string> ::= <unquoted_string>
             <quoted_string>

<unquoted_string> ::= <lower_case_alphabetic_character>
                      <unquoted_string><alpha_numeric_character>

<quoted_string> ::= <double_quoted_string>
                    <single_quoted_string>

<double_quoted_string> ::= ""
                           "<character_string>"

<single_quoted_string> ::= ''
                           '<character_string>'

<character_string> ::= <character>
                       <character_string><character>

<alpha_numeric_character> ::= <alphabetic_character>
                              <numeric_character>

<alphabetic_character> ::= <lower_case_alphabetic_character>
                           <upper_case_alphabetic_character>

<lower_case_alphabetic_character> ::= a b ... z $

<upper_case_alphabetic_character> ::= A B ... Z _ '

<numeric_character> ::= 0 1 ... 9

<number> :: <integer>
            <real>

<integer> ::= <positive_integer>
             +<positive_integer>
             -<positive_integer>

<positive_integer> ::= <numerics>

<numerics> ::= <numeric_character>
               <numerics><numeric_character>

<real> ::= <positive_real>
          +<positive_real>
          -<positive_real>

<positive_real> ::= <fixed_point_constant>
                    <fixed_point_constant><exponent>

<fixed_point_constant> ::= <numerics>.<numerics>
                                     .<numerics>

<exponent> ::= <exponent_letter>
               <exponent_letter><integer>

<exponent_letter> ::= E
                      e


Notes:

A <character> is any single Ascii character, except for a single-quote
(') within a <single_quoted_string> or for a double-quote (") within a
<double_quoted_string>.

When it is necessary to include a single-quote character within a
<single_quoted_string>, it can be represented by the digraph  '' .
Similarly for a double-quote character within a <double_quoted_string>.

The characters underscore (_) and single quote (') have been declared <upper_case_alphabetic_character> for convenience, since they may appear within or at the end of an <unquoted_string>.



This document is licensed under Gnu General Public License - Version 3 

     http://www.nongnu.org/efcp/gnu-gpl3.html