&#39; | &#39;!=&#39; | &#39;&lt;&#39; | &#39;&lt;=&#39; | &#39;&gt;&#39; | &#39;&gt;=&#39;)

index ::= ?(expression | expression &#39;:&#39; | &#39;:&#39; expression
        | expression &#39;:&#39; expression)

indexes ::= index % &#39;,&#39;

integer_literal ::= [0-9]+

real_literal ::= integer_literal &#39;.&#39; [0-9]* ?exp_literal
               | &#39;.&#39; [0-9]+ ?exp_literal
               | integer_literal exp_literal

exp_literal ::= (&#39;e&#39; | &#39;E&#39;) ?(&#39;+&#39; | &#39;-&#39;) intege