[[Property:title|Eiffel polynomial parser]]
[[Property:weight|0]]
[[Property:uuid|63f0e737-4ad7-c574-3bbc-05e005815785]]
In the directory '''$ISE_EIFFEL/examples/parse''' you will find a system that implements a processor for a grammar describing a simple language for expressin polynomials. A typical document in this language is the line 
<code>
x;y: x * (y + 8 - (2 * x))
</code>
The beginning of the line, separated from the rest by a colon, is the list of variables used in the polynomial, separated by semicolons. The rest of the line is the expression defining the polynomial. The grammar can be described with the following grammar: 
<code>
LINE      = VARIABLES ":" SUM 
VARIABLES = VAR .. ";" 
SUM       = DIFF .. "+" 
DIFF      = PRODUCT .. "-" 
PRODUCT   = TERM .. "*" 
TERM      = SIMPLE_VAR | INT_CONSTANT | NESTED
NESTED    = "(" SUM ")" </code>
This grammar assumes a terminal '''VAR''', which must be defined as a token type in the lexical grammar. The other terminals are keywords, shown as strings appearing in the double quotes, for example "+". 
When compiling the example, the executable '''process(.exe)''' is created. When executing the program, it will prompt for the name of a file with a polynomial description, reads a polynomial from the given file, prompts for integer values of the variables, and evaluates the polynomial.