Re: How change grammar to equivalent LL(1) ?

Am 23.12.2019 um 00:55 schrieb Andy:
> Obviously if is possible.
> In Polish Wikipedia can we read, that even very simple grammar:
> expr->number '+' expr
> expr->number
> is not LL(1) bacause we must see '+' to distinguish
>
> But
> is posssible equivalent grammar:
> expr -> number optPlusExpr
> optPlusExpr -> epsilon
> optPlusExpr ->'+' expr
>
> What are general rules to change grammar to equivalent LL(1) grammar if possible?


Use EBNF:
      expr -> number { '+' expr }
or
      expr -> number { '+' number }


EBNF or "railroad diagrams" typically translate directly into LL
top-down parsers. Many problems vanish when the grammar does not allow
for too much freedom causing inobvious problems. E.g. in EBNF only a
single derivation of a (left hand) nonterminal is allowed.


DoDi

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