Re: [Caml-list] Should -strict-sequence become the default?

[Yaron Minsky <yminsky@janestreet.com>]

There are cases that the warning doesn't catch but should.  Here's an
example of a case that you'd like to catch.

# let z f = f (); 3;;
val z : (unit -> 'a) -> int = <fun>

With strict-sequence, this will instead compile to:

# let z f = f (); 3;;
val z : (unit -> unit) -> int = <fun>

I think the strict-sequence behavior is strictly preferable.

y

On Sun, Oct 27, 2013 at 2:27 PM, John Whitington
<john@coherentgraphics.co.uk> wrote:
> Hi,
>
>
> Yaron Minsky wrote:
>>
>> Back in 3.12.1, a flag, -strict-sequence, was added that require that
>> the left-hand side of a sequence returns unit.  I suspect there's
>> broad agreement that -strict-sequence is the better default, but that
>> the old behavior has been left in place by default for compatibility
>> reasons.  I wonder if in the next major release, it would make sense
>> to make -strict-sequence the default, and have a flag for enabling the
>> old behavior.
>>
>> To say the obvious, such a change would be of no value to experienced
>> people and organizations that know how to set up the compiler to their
>> liking, but can be of real value to newcomers to the language.
>
>
> Isn't this covered (as a warning not an error) by warnings 5 & 10, both of
> which are default?
>
> Although the manual does say, rather ominously...
>
> "Note that warnings 5 and 10 are not always triggered, depending on the
> internals of the type checker."
>
> Does that caveat also apply to -strict-sequence? If not, why not, and could
> its implementation be back-ported to fix up warnings 5 and/or 10?
>
> feast:~ john$ ocaml -strict-sequence
>         OCaml version 4.01.0
>
> # let f x = x + 1;;
> val f : int -> int = <fun>
> # f 1; 0;;
> Error: This expression has type int but an expression was expected of type
> unit
>
> feast:~ john$ ocaml
>         OCaml version 4.01.0
>
> # let f x = x + 1;;
> val f : int -> int = <fun>
> # f 1; 0;;
> Warning 10: this expression should have type unit.
> - : int = 0
>
> The warning text for warning 10 could be changed to:
>
> "Warning 10: this expression should have type unit. If this is intended,
> consider using the 'ignore' function."
>
> Cheers,
>
> --
> John Whitington
> Director, Coherent Graphics Ltd
> http://www.coherentpdf.com/
>