ded, along with construction of a
scanner capable of breaking characters up into meaningful tokens (such
as keywords, numbers, and special symbols).</p><p> 

As a simple example, consider a 
system for evaluating simple arithmetic expressions over integers.  
This system would read expressions from standard input (each terminated 
with a semicolon), evaluate them, and print the result on standard output.  
A grammar for the input to such a system might look like: </p><pre>  expr_list ::= expr_list expr_part