[Caml-list] unused variables warning

[Caml-list] unused variables warning

[Pixel]

Is there any way to ask ocamlc for an "unused variable" warning?

let f x =
   let x' = <...> in
   x

would issue something like

File "test.ml", line 2, characters 3-18:
Unused variable x'


thanks, cu Pixel.
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Re: [Caml-list] unused variables warning

[Vitaly Lugovsky]

On Sat, 28 Apr 2001, Pixel wrote:

> Is there any way to ask ocamlc for an "unused variable" warning?
>
> let f x =
>    let x' = <...> in
>    x
>
> would issue something like
>
> File "test.ml", line 2, characters 3-18:
> Unused variable x'

 It's "unused" and can be optimized out only when <...> is a pure
functional statement (not changing global state). There is no clean way to
figure this out, since we can use foreign functions, and "purity" is not
specified in a module signature. 'tis a very interesting suggestion:
specify pure functional and state-changing functions in signatures
(automaticaly or manualy), and use this info for a better optimizations.


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Re: [Caml-list] unused variables warning

[Pixel]

Vitaly Lugovsky <vsl@ontil.ihep.su> writes:

[...]

> > let f x =
> >    let x' = <...> in
> >    x
> >
> > would issue something like
> >
> > File "test.ml", line 2, characters 3-18:
> > Unused variable x'
> 
>  It's "unused" and can be optimized out only when <...> is a pure
> functional statement (not changing global state). 

even if the <...> is unpure, caml could warn that x' is unused. It doesn't mean
in any way that computing x' is unnecessary.

and caml should not warn for

let _x' = <...> in

> There is no clean way to
> figure this out, since we can use foreign functions, and "purity" is not
> specified in a module signature. 'tis a very interesting suggestion:
> specify pure functional and state-changing functions in signatures
> (automaticaly or manualy), and use this info for a better optimizations.

that would be cool, but it's much more complicated than my simple suggestion :)


cu Pixel.
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Re: [Caml-list] unused variables warning

[Marcin 'Qrczak' Kowalczyk]

Sun, 29 Apr 2001 12:15:24 +0400 (MSD), Vitaly Lugovsky <vsl@ontil.ihep.su> pisze:

> It's "unused" and can be optimized out only when <...> is a pure
> functional statement (not changing global state).

If it's not, I would not bind its result to a variable but to _.

-- 
 __("<  Marcin Kowalczyk * qrczak@knm.org.pl http://qrczak.ids.net.pl/
 \__/
  ^^                      SYGNATURA ZASTĘPCZA
QRCZAK

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Re: [Caml-list] unused variables warning

[Sven LUTHER]

On Sun, Apr 29, 2001 at 11:58:22AM +0200, Pixel wrote:
> Vitaly Lugovsky <vsl@ontil.ihep.su> writes:
> 
> [...]
> 
> > > let f x =
> > >    let x' = <...> in
> > >    x
> > >
> > > would issue something like
> > >
> > > File "test.ml", line 2, characters 3-18:
> > > Unused variable x'
> > 
> >  It's "unused" and can be optimized out only when <...> is a pure
> > functional statement (not changing global state). 
> 
> even if the <...> is unpure, caml could warn that x' is unused. It doesn't mean
> in any way that computing x' is unnecessary.
> 
> and caml should not warn for
> 
> let _x' = <...> in

I guess you mean just :

let _ = <...> in 

?

Friendly,

Sven Luther
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Re: [Caml-list] unused variables warning

[Pixel]

Sven LUTHER <luther@dpt-info.u-strasbg.fr> writes:

> > even if the <...> is unpure, caml could warn that x' is unused. It doesn't mean
> > in any way that computing x' is unnecessary.
> > 
> > and caml should not warn for
> > 
> > let _x' = <...> in
> 
> I guess you mean just :
> 
> let _ = <...> in 

well, no. In fact i thought "_x" and "_" were the same, discarded,
non-accessible variables. I'm wrong on this.

the manual recommend not to use _xxx variables, otherwise it could have been a
way to write things like:

let _no_warning_but_meaningful_name = <...> in

but it would be another rule to learn: ``no warning for unused variables
starting with _'' (which is just what Haskell is doing).

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[Caml-list] Re: unused variables warning

[Pixel]

I've asked the following question one year ago:

> Is there any way to ask ocamlc for an "unused variable" warning?
> 
> let f x =
>    let x' = <...> in
>    x
> 
> would issue something like
> 
> File "test.ml", line 2, characters 3-18:
> Unused variable x'

I got an answer from Pascal Brisset sending me a nice incomplete piece
of code doing this. After a small adaptation, I've been using it with
3.04.

When "updating" it to 3.06, i tried to integrate in mandrake's package
to ease my use of it:
- i've added it when all warnings are enabled (-w A)
- it's quite ugly, i've added the various things to make it compile on
3.06 without knowing what should be done. At least it somewhat works :)
- i've dropped a functionality from Pascal Brisset's tool: it only
checks local variables, not modules variables&functions. It was easier
for me and does the checks I need (since my .mli are mostly
auto-generated).
- the comments from Pascal Brisset still apply
  - it is uncomplete (it does not handle local modules ...)
  - warning are not issued for identifiers starting with an underscore.

So if it interests someone :)

The patch on ocaml 3.06:
http://people.mandrakesoft.com/~prigaux/ocaml-3.06-add-warning-for-unused-local-variables.patch

The tool on ocaml 3.04:
http://people.mandrakesoft.com/~prigaux/warn_unused.make
http://people.mandrakesoft.com/~prigaux/warn_unused.ml


(special thanks to Pascal Brisset of course)
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