Simplification of CFG what data structure

[zizi]

hi there everybody,

I have to make a program that gets a string and then finds out if it is accepted by the CFG(cintext free grammer),
I want to first do the Simplification of CFG but I really don't know what data structure I have to use,
for example I want to get rid of useless symbols(those that do
not participate in any derivation of a terminal string.)
here i have the file that keeps the grammer for example
S>AB
S>a
A>b
then I have to get ride of B cuz not genarating termenals so the grammer would be :
S>a
A>b
then get rid of A cuz not reachable from S,so:
S>a

so how cud I do this with coding?

thank you

[apegram]

Eric Lippert of the C# compiler team is the midst of writing a series on binary trees, arbitrary trees, and "every program there is" along these very same lines.

http://blogs.msdn.com/ericlippert/archive/2010/04/19/every-binary-tree-there-is.aspx
http://blogs.msdn.com/ericlippert/archive/2010/04/22/every-tree-there-is.aspx
http://blogs.msdn.com/ericlippert/archive/2010/04/26/every-program-there-is-part-one.aspx
http://blogs.msdn.com/ericlippert/archive/2010/04/29/every-program-there-is-part-two.aspx
http://blogs.msdn.com/ericlippert/archive/2010/05/03/every-program-there-is-part-three.aspx
http://blogs.msdn.com/ericlippert/archive/2010/05/06/every-program-there-is-part-four.aspx
http://blogs.msdn.com/ericlippert/archive/2010/05/10/every-program-there-is-part-five.aspx

Part 6 will probably be up Thursday.

[zizi]

thanks for your help,
I look at these pages,so the implementation is with a tree,
I'll read all,nice information,