Re: Q2. Why do you split a monolitic grammar into the lexing and parsing rules?

"valentin tihomirov" <spam@abelectron.com> wrote in message
> Looks like this is a group discussing parsing-translating issues as
> a matter of compiler front-ends. So, the problem is to enable using
> reserwed keywords as identifiers. ....


> So, I do not understand why do we need the artificial obstacle, the
> 2nd level?


> [Try writing a single-level parser that disregards spaces and
> optional spaces in the usual way. A separate lexer makes that a
> whole lot easier. -John] >


The answer to your subject question for me is "to reduce complexity".
There was (many years ago) a tradition in modular programming that no
function should be longer than a single printed page. It is a good
measure of what an ordinary human can comprehend easily. Well, we
(almost never) use printed pages anymore and my rule is that a
function shouldn't be longer than a few screens. Applying the same
principle to grammars, once a grammar gets beyond a certain point in
complexity it's easier to comprehend what's going on (and much easier
to find problems) if there's a split into the lexical and syntactical
halves -- at least for me.


        Norm

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