[Caml-list] infinity matches all

[Caml-list] infinity matches all

[Yaron Minsky]

Can anyone explain the following behavior of match when used with infinity?

# match "foo" with infinity -> "bar";;
- : string = "bar"

This shouldn't even typecheck.  It seems to treat infinity as equivalent
to "_".  This behavior comes up in version 3.06.

Yaron


-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners

Re: [Caml-list] infinity matches all

[Oleg Trott]

On Monday 25 August 2003 10:12 am, Yaron Minsky wrote:
> Can anyone explain the following behavior of match when used with infinity?
>
> # match "foo" with infinity -> "bar";;
> - : string = "bar"
>
> This shouldn't even typecheck.  It seems to treat infinity as equivalent
> to "_".  This behavior comes up in version 3.06.

This is ugly. The same happens with  `nan' , BTW.

-- 
Oleg Trott <oleg_trott@columbia.edu>

-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners

Re: [Caml-list] infinity matches all

[Xavier Leroy]

> Can anyone explain the following behavior of match when used with infinity?
> 
> # match "foo" with infinity -> "bar";;
> - : string = "bar"
> 
> This shouldn't even typecheck.  It seems to treat infinity as equivalent
> to "_".  This behavior comes up in version 3.06.

This is probably in the FAQ somewhere.  What confuses you is that this
occurrence of "infinity" is just a variable that is bound by the
matching; it's not a constructor, and it's not a constant.  Hence, you
code is equivalent (by renaming) to

        match "foo" with s -> "bar";;

and indeed to

        match "foo" with _ -> "bar";;

since _ behaves like a variable that isn't referenced in the r.h.s.

If you intend to match against the value of floating-point infinity, do

        match e with x when x = infinity -> ...

- Xavier Leroy

-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners

Re: [Caml-list] infinity matches all

[Mattias Waldau]

There is a patch which warns for unused variables. Then you would have 
got the message that the variable "infinity" isn't used. It regulary 
finds bugs for me.

-- Mattias

Xavier Leroy wrote:
>>Can anyone explain the following behavior of match when used with infinity?
>>
>># match "foo" with infinity -> "bar";;
>>- : string = "bar"
>>
>>This shouldn't even typecheck.  It seems to treat infinity as equivalent
>>to "_".  This behavior comes up in version 3.06.
> 
> 
> This is probably in the FAQ somewhere.  What confuses you is that this
> occurrence of "infinity" is just a variable that is bound by the
> matching; it's not a constructor, and it's not a constant.  Hence, you
> code is equivalent (by renaming) to
> 
>         match "foo" with s -> "bar";;
> 
> and indeed to
> 
>         match "foo" with _ -> "bar";;
> 
> since _ behaves like a variable that isn't referenced in the r.h.s.
> 
> If you intend to match against the value of floating-point infinity, do
> 
>         match e with x when x = infinity -> ...
> 
> - Xavier Leroy
> 
> -------------------
> To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
> Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> 



-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners