Deprecating fromIntegral

[dominic at steinitz.org]

> On 22 Sep 2017, at 13:43, Dominic <dominic.steinitz at blueyonder.co.uk> wrote:
> 
> Coincidentally, I was playing with this a few days ago. I didn’t seem to have to do anything to get a warning.
> 
>> GHCi, version 8.0.2: http://www.haskell.org/ghc/  :? for help
>> Prelude Data.Word> :m Data.Int
>> Prelude Data.Int> 0x80000000 :: Int32
>> 
>> <interactive>:27:1: warning: [-Woverflowed-literals]
>>    Literal 2147483648 is out of the Int32 range -2147483648..2147483647
>>    If you are trying to write a large negative literal, use NegativeLiterals
>> -2147483648
>> Prelude Data.Int> :set -XNegativeLiterals
>> Prelude Data.Int> 0x80000000 :: Int32
>> 
>> <interactive>:29:1: warning: [-Woverflowed-literals]
>>    Literal 2147483648 is out of the Int32 range -2147483648..2147483647
>> -2147483648
> 
> I am not clear why it wanted me to use NegativeLiterals but still give the same warning. Does anyone understand the intent here?
> 
>> Message: 1
>> Date: Fri, 22 Sep 2017 14:14:12 +0200
>> From: Herbert Valerio Riedel <hvriedel at gmail.com>
>> To: Niklas Hambüchen <mail at nh2.me>
>> Cc: Haskell Libraries <libraries at haskell.org>
>> Subject: Re: Deprecating fromIntegral
>> Message-ID:
>> 	<CAOFsArv1rDT1=KsM_z1vDOf_CW-jamOT8nzGzHk3VnxuEvjMug at mail.gmail.com>
>> Content-Type: text/plain; charset="UTF-8"
>> 
>> ...there's one minor detail I'd like to point out as it doesn't seem
>> to have been mentioned so far:
>> 
>> On Thu, Sep 21, 2017 at 5:34 PM, Niklas Hambüchen <mail at nh2.me> wrote:
>> 
>>> (Though, in practice the current `fromInteger is not partial, e.g.
>>> `(fromInteger 256 :: Word8) == 0` without error
>> 
>> That's true. However, here's something you can do already now with
>> recent GHCs which gives turns literal-overflows GHC is able to detect into
>> hard compile errors:
>> 
>> 
>> $ ghci -Wall -Werror=overflowed-literals
>> GHCi, version 8.2.1: http://www.haskell.org/ghc/  :? for help
>> Prelude> (256 :: Data.Word.Word8) == 0
>> 
>> <interactive>:1:2: warning: [-Woverflowed-literals]
>>     Literal 256 is out of the GHC.Word.Word8 range 0..255
>> 
>> <no location info>: error:
>> Failing due to -Werror.
>> Prelude>
>> 
>> 
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> 

Dominic Steinitz
dominic at steinitz.org
http://idontgetoutmuch.wordpress.com