such ambiguities ... do not stop us from expressing whichever of the choices perl actually makes in BNF.

Yeah? Try it.

The problem is that in order to resolve the ambiguity (i.e., in order to select the choice perl actually makes, as you put it) you have to have access to information about the surrounding context, information that gets lost when reducing the surrounding syntax to BNF. 

   s ;; split / , / ;; s ,$, ; , ; print eval;

[download]

Don't make me turn this into a self-modifying quine.

Incidentally, a lot of Lisp or Scheme programmers recoil in horror when they find out that Perl's grammar is not context-free. "If it's not possible to determine what a given syntactic construct means independent of context, how could anyone ever keep track of what a piece of a program is doing?" Well, that's the problem BNF has. In practice, this is not generally a problem for programmers who know the language, but it gives overly simple parsers fits.

In reply to Re: Perl not BNF-able?? by jonadab
in thread Perl not BNF-able?? by anonymized user 468275

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