Re: [Caml-list] infinity matches all

[Mattias Waldau <mattias.waldau@abc.se>]

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
> 
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