CPS 1 Using syntax rules to derive a sample program.

	program train;
	var
		gate:string;
	begin
	writeln('Is crossing gate up or down?');
	readln(gate);
	if gate = 'down' then
		begin
  		writeln('Watch the train go by.');
		end
	else
		begin
		writeln('We beat the train this time!');
		end;
	readln;
	end.

#14	<program> -> program <identifier>;
			<variable declarations>
			<compound statement>.

#1	<program> -> program train;
			<variable declarations>
			<compound statement>.

#12	<program> -> program train;
			var
				<identifier>:<type>;
			<compound statement>.

#1,13	<program> -> program train;
			var
				gate: string;
			<compound statement>.

#7	<program> -> program train;
			var
				gate: string;
#7			begin
			<statement>;
			<statement>;
			<statement>;
			<statement>;
			end.

	<program> -> program train;
			var
				gate: string;
			begin
#4			writeln(<string expression>);
#5			readln(<identifier>);
#8			if <boolean expression> then
				<compound statement>
			else
				<compound statement>;
#6			readln;
			end.

	<program> -> program train;
			var
				gate: string;
			begin
#3			writeln('Is crossing gate up or down?');
#1			readln(gate);
#10			if gate = 'down' then
				<compound statement>
			else
				<compound statement>;
			readln;
			end.

	<program> -> program train;
			var
				gate: string;
			begin
			writeln('Is crossing gate up or down?');
			readln(gate);
			if gate = 'down' then
#7				begin
				<statement>;
				end
			else
#7				begin
				<statement>;
				end;
			readln;
			end.

	<program> -> program train;
			var
				gate: string;
			begin
			writeln('Is crossing gate up or down?');
			readln(gate);
			if gate = 'down' then
				begin
#4				writeln(<string expression>);
				end
			else
				begin
#4				writeln(<string expression>);
				end;
			readln;
			end.

	<program> -> program train;
			var
				gate: string;
			begin
			writeln('Is crossing gate up or down?');
			readln(gate);
			if gate = 'down' then
				begin
#3				writeln('Watch the train go by.');
				end
			else
				begin
#3				writeln('We beat the train this time!');
				end;
			readln;
			end.