FIRST function computation problem.

Hi,


I have a problem with FIRST function for 1 lookahead symbol evalation.
To lookup such the symbols for some nonterminal A I am doning follows:


1. go through all rules that left part is A. Here I do following:
a) If I have rule A --> aB, where a is terminal. I just add this
terminal to lookahead set for A.
b) If I have rule A --> e, where e is epsilon, I add e to lookahead
set for A.
c) If I have rule A --> B C ... where B - nonterminal, I at first
compute the lookahead set for B, if B's lookahead set contains
epsilon, check C and etc. I found that recursive function here is the
best. But I do not know how to work with rules like follows: A --> B,
B --> C A D... To compute lookahead set for A I have to at first
compute lookaheads for B, but if lookaheads for C contain epsilon I
need to know the same about A to understand do checking of D or
not...


Please, help to decide this problem and there may be the good FIRTS
computaion algorithm?


Thanks,
Vladimir.

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