It is pretty straightforward to write a recursive descent parser based on a BNF grammar by hand: make every nonterminal a procedure that parses that nonterminal, and have it recursively invoke other procedures whenever the BNF grammar refers to other nonterminals. Parse terminal symbols any way you see fit (a separate lexer that tokenizes the input is easy to write ad hoc or by using regular expressions). See any language/automata theory book or compiler technology book for more info.

In other news

I have taken over the TeXmalli document from liw. It is a sample LaTeX document written in Finnish.