% here's the example

 \input generic.tex

 \input bnf.tex

 \begingrammar

 %		

 <input>:	{$\phi$};

 		<statement>.\par

 <statement>:	"$\{$" <compound> "$\}$" [";"] ;

 		<single> [";"] ;

 		";".

 <compound>:	<single> ";" <compound> ;

 		<single>.

 <single>:	"if" "(" <expression> ")" <statement> ["else" <statement>];

 		"case" "$\{$" <case-body> "$\}$";

 		"for" "(" <expression> ";" <expression> ";" <expression> ")",

 			<statement>;

 		"while" "(" <expression> ")" <statement>;

 		"do" <expression> "while" "(" <expression> ")";

 		"sum" "(" <expression> ";" <expression> ")" <statment>;

 		"product" "(" <expression> ";" <expression> ")" <statment>;

 		"break";

 		"continue";

 		"return" <expression>;

 		"clear";

 		"load" <expression>;

 		"save" <expression>;

 		"release" <expression>;

 		"show" ["variables" | "functions" | "set" | "all" | <expression>];

 		"set"  ["prompt" | "precision"] [<expression>];

 		<equation>.

 <case-body>:	"case" <expression> ":" <compound> <case-body>;

 		 "default:" <compound>

 <equation>:	<var> "=" <expression>;

 		<var>"[" <selector> "]" = <expression>;

 		<function> = <input>;

 		<expression>.

 <selector>:	<factor> "," <factor>;

 		<factor> ",";

 		"," <factor>.

 <expression>:	<term> "+" <expression>;

 		<term> "--" <expression>.		

 <term>:		<factor> <operator> <term>.

 <factor>	<pre-op> <factor$'$> <post-op>.

 <factor$'$>:	<number>;

 		"+" <number>;

 		"--" <number>;

 		"(" <number> ")";

 		<variable>;

 		<variable>"[" <selector> "]";

 		<string>;

 		<matrix>;

 		<function>.

 <pre-op>:	"++" | "--{\kern 1pt}--" | "$\sim$" | "!".

 <post-op>:	"$\uparrow$" <factor> 

 		| "**" <factor>;

 		"++" | "--{\kern 1pt}--" | "!".		

 <matrix>:	"[" <row-list> "]".

 <row-list>:	"[" <value-list> "]" [","] <row-list>;

 		"[" <value-list> "]" [","] <row-list>;

 		<value-list>.

 <value-list>:	[ <string> ] <expression> "," <value-list>;

 		[ <string> ] <expression>.

 <function>:	<variable> "(" <arg-list> ")".

 <arg-list>:	$\phi$;

 		<variable> "," <arglist>;

 		"\dots".

 <string>:	" `` "  <anything> " '' ".

 <number>:	<real-number>;

 		"$\{$" <real-number> "," <real-number> "$\}$";

 		{$\backslash$}b[01][01]+;

 		{$\backslash$}o[07][07]+;

 		\$[0-9A-Fa-f][0-9A-Fa-f]+.

 %<real-number>:	[\+--]?[0-9][0-9]+[\.[0-9]+]?[[eE][0-9][0-9]+].

 <operator>:	"*" |	 "/"	|     "$\backslash$"	| "\%";

 		"==" |	 "!="	|     "$>$" 		| "$<$"  

 		| "$<$=" | "$>$=";

 		"\ul ="	| "\ul !=" |  "\ul $<$" | "\ul $>$" 

 		| "\ul$<$=" | "\ul$>$=";

 		"\&"	 | "$\vert$"  | "$\uparrow\uparrow$";

 		"\&\&"	| "$\Vert$"  | "\ul$\uparrow$".

 \endgrammar

 \bye