type t = ()

type t = ()

[Richard Jones]

I had a program where a type was accidentally defined as (), and the
error messages confused me for ages until I worked out what was going
on ...

$ ocaml
        Objective Caml version 3.08.3

# type dummy = ();;
type dummy = ()
# let () = Printf.printf "hello";;
This expression has type unit but is here used with type dummy

Rich.

-- 
Richard Jones, CTO Merjis Ltd.
Merjis - web marketing and technology - http://merjis.com
Team Notepad - intranets and extranets for business - http://team-notepad.com

Re: type t = ()

[Vincenzo Ciancia]

Richard Jones wrote:

> # type dummy = ();;
> type dummy = ()
> # let () = Printf.printf "hello";;
> This expression has type unit but is here used with type dummy
> 

It seems that the compiler accepted "()" as a type constructor, so now every
instance of "()" is the only constructor of type "dummy" e.g.

# type d = () of int;;
type d = () of int
# () 3;;
- : d = () 3

V.

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Re: [Caml-list] Re: type t = ()

[Wolfgang Lux]

Vincenzo Ciancia wrote:

> Richard Jones wrote:
>
>> # type dummy = ();;
>> type dummy = ()
>> # let () = Printf.printf "hello";;
>> This expression has type unit but is here used with type dummy
>>
>
> It seems that the compiler accepted "()" as a type constructor, so now 
> every
> instance of "()" is the only constructor of type "dummy" e.g.

Sorry for nitpicking, but in this case () is a *data* constructor.
I guess, Rich would have been more happy if OCaml did recognize ()
as a type constructor in this example.

However, I guess one cannot do much about this in OCaml since () is
a legitimate data constructor name. The problem really is that the
(O)Caml designers chose to overload the type keyword for defining
algebraic data types as well as type abbreviations. Compare with SML
and Haskell where different keywords are used.

Regards
Wolfgang

Re: [Caml-list] type t = ()

[Jonathan Bryant]

Is this a question or a brief rant...? :)

On Thu, 2005-06-09 at 17:22, Richard Jones wrote:
> I had a program where a type was accidentally defined as (), and the
> error messages confused me for ages until I worked out what was going
> on ...
> 
> $ ocaml
>         Objective Caml version 3.08.3
> 
> # type dummy = ();;
> type dummy = ()
> # let () = Printf.printf "hello";;
> This expression has type unit but is here used with type dummy
> 
> Rich.
> 
> -- 
> Richard Jones, CTO Merjis Ltd.
> Merjis - web marketing and technology - http://merjis.com
> Team Notepad - intranets and extranets for business - http://team-notepad.com
> 
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Re: [Caml-list] type t = ()

[Richard Jones]

On Thu, Jun 09, 2005 at 07:43:44PM -0400, Jonathan Bryant wrote:
> Is this a question or a brief rant...? :)

Sort of a brief rant combined with a bug report :-)

Rich.

-- 
Richard Jones, CTO Merjis Ltd.
Merjis - web marketing and technology - http://merjis.com
Team Notepad - intranets and extranets for business - http://team-notepad.com

Re: [Caml-list] type t = ()

[Florian Hars]

Richard Jones wrote:
> Sort of a brief rant combined with a bug report :-)

But the bug is in the same class as:

# let (-) = ( * );;
val ( - ) : int -> int -> int = <fun>
# 1 + 2 - 3;;
- : int = 9

No?

Yours, Florian.

Re: [Caml-list] type t = ()

[Jon Harrop]

On Friday 10 June 2005 14:02, Florian Hars wrote:
> But the bug is in the same class as:
>
> # let (-) = ( * );;
> val ( - ) : int -> int -> int = <fun>
> # 1 + 2 - 3;;
> - : int = 9
>
> No?

Isn't that exactly what you'd expect?

  (1 + 2) * 3 = 9

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
Objective CAML for Scientists
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