Re: precedences vs. hierarchy

On Mon, 6 Jun 2016 09:08:56 +0200, Andreas Schramm
<bassobajo@gmail.com> wrote:


>for specifying the syntax of operator expressions
>with multiple levels of precedences,
>there are essentially two approaches:
>(i) by precedence and associativity declarations, and
>(ii) by a hierarchy of non-terminals.
>Both approaches have been known and in use for decades.
>
>My question is:
>Are there trends in the public opinion
>in favor of one of them over the other?
>Or are they equally respected approaches?


In general, precedence is shorter and easier to define. However when
there are many levels, associativity can be hard to get right, and
incorrect associativity chaining can be difficult to debug.


Non-terminal operator heirarchies are more work to define, but they
usually are easier to fix when associativity is wrong.


Your tools will dictate which approach you can use: few (if any) LL
tools support operator precedence, while all (?) LR tools do support
it. If your tool supports precedence, you still can choose to use an
explicit heirarchy instead if that works better for you.


What matters most is getting your grammar right ... don't worry too
much about what other people think of it.


Hope this helps,
George

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