[grammarians] ambiguity with method call?

[Terence Parr]

On Nov 29, 2005, at 11:47 PM, Ryan Davis wrote:

>
> On Nov 29, 2005, at 12:59 PM, Terence Parr wrote:
>
>> Howdy,
>>
>> What does
>>
>> foo [1]
>
> sudo gem install ParseTree (!!)
>
> % echo "foo [1]" | parse_tree_show -f
> ...
> [:fcall, :foo, [:array, [:array, [:lit, 1]]]]
>
> without any other context to go on, it is assumed it is an fcall,  
> in other contexts it could be an lvar, dvar, or a regular call.
>
> You should also do a gem unpack ParseTree and look through the unit  
> tests. That might answer quite a few of your questions as well.

Yep.  Thanks, Ryan.

Here's the thing.  The impl does not specify the language definition;  
i've seen mistakes in C compilers.  My point is that the language  
rules as described everywhere I look could easily be seen to  
interpret foo[1] in two ways:

(foo)[1]

and

foo([1])

even when we know foo is a function call.  how could it not?  There  
is no syntax to distinguish.  Remember that structure imparts  
meaning.  Just because his implementation picks one doesn't mean  
there isn't a real ambiguity here.  For example, C++ clearly  
identifies the ambiguity between decl and expr statements and says in  
the book that if some input can be either, choose decl (it's still a  
bad thing, but it's known and specified).

Languages do have ambiguities such as the if-then-else bugaboo, but  
it needs to be clearly outlined rather than just biting somebody.   
More importantly, computer languages should be defined as  
deterministically/unambiguously as possible.  It's already bad enough  
in ruby that I have to look backwards to see how it was used first  
lexically (particularly when there are two interpretations possible  
given foo=1 and def foo).  Adding in this unspecified preference to  
resolve the ambiguity is pretty rough on a guy.  It's a bug in hiding  
waiting to bite you 2 years hence when that code execs and gives you  
a runtime type exception.

All that said, the point of this exercise is probably to get a real  
spec driven from a real grammatical description.  Am I the first  
person to run across this ambiguity before?

Ter