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partial application warning unreliable?
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Date: 2005-12-08 (07:12)
From: skaller <skaller@u...>
Subject: Re: [Caml-list] partial application warning unreliable?
On Thu, 2005-12-08 at 12:10 +0900, Jacques Garrigue wrote:
> From: skaller <skaller@users.sourceforge.net>
> >     method add_nonterminal (s:string) (sr:range_srcref) (toks:
> > Flx_parse.token list) (term:ast_term_t) =
> > 
> > ...
> >     state#add_nonterminal tok (Flx_srcref.slift sr) t;
> > 
> > Method has 4 arguments, but the call applies to only 3.
> > 
> > Woops, no warning!! Bad! This error of mine caused a serious
> > bug -- the method call didn't do anything!
> Wait a minute, is there anything after the semicolon?

yes, it is followed by an empty list []

> The point is that a trailing semicolon at the end of a method
> definition does nothing: it still returns the result of the previous
> expression!

That's a bit weird, but I guess the decision is somewhat
arbitrary .. I actually wonder if using camlp4 changes this
result (since I guess it is an artefact of the parser/grammar
rather than a deliberate  choice .. :)

> I wonder whether this behaviour is good or not, but this also means
> that there is no reason to have a warning here.

IMHO an expression on the LHS of a semicolon expression
(possibly excluding the degenerate case the RHS is empty)
should have type unit**, and it should be *hard error* not a warning
if it doesn't: the ignore(expr) function can be used
to suppress the error if required.

** as you know I think the type should be void,
not unit. Other systems (such as FISh) has a special
type such as 'command' for this. But whichever type
is chosen, Ocaml should be *strict* about it. It is
strict everywhere else .. I don't understand why it
isn't strict here.

> If there is an expression after the semicolon, and you have no
> warning, then file a bug report: the type system is supposed to detect
> all partial applications in statements, except for functions whose
> result is a polymorphic type variable.

I don't have a reduced example though, and the error is
already fixed in my code. 

> By the way, your other example with classes is wrong:
> # class cc = object (self) 
>     method f x y = x + y 
>     method g () = self#f 1;  
>   end;;
> class cc :
>   object method f : int -> int -> int method g : unit -> int -> int end
> No warning, for the reason stated above: the semicolon does nothing.

Ouch .. you're right -- I actually DID get an error F .. jumbled
up inside THREE copies of the text the top level printed trying
to underline the error. The toplevel is very sick ..

BTW: the error flags documentation is very confusing:

     A/a enable/disable all warnings
     X/x enable/disable all other warnings

other than what? I am using -w yz but STILL get
warning X, unused function argument .. some of this
happens in Frontc/CIL which I'm using and I would like
to minimise patches.

BTW: what is this for?

     S/s enable/disable non-unit statement

Isn't that going to be F partial application 99% of the time?
If I turn off F, will I get S instead?

John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net