Is deprecation as bad as removal?

David Feuer david.feuer at
Wed Feb 25 00:04:27 UTC 2015

One option is to recognize two kinds of deprecation

1. Traditional GHC style: deprecated = we will remove this soon
2. Traditional some-other-places style: deprecated = we advise against
using this

On Tue, Feb 24, 2015 at 6:55 PM, Greg Weber <greg at> wrote:
> Even if warnings are treated as errors, it is not correct because you can
> turn off deprecation warnings. To be fine-grained you can create a single
> module where deprecated things are imported and then re-exported, but that
> module has deprecation warnings turned off. Certainly that is extra work,
> but it is easier than most would imagine.
> On Tue, Feb 24, 2015 at 3:35 PM, Ben Millwood <haskell at>
> wrote:
>> I'm going to grab this quotation from a recent thread discussing removal
>> of fromJust:
>> On Tue, Feb 24, 2015 at 02:32:08PM -0500, Edward Kmett wrote:
>>> I'm personally pretty strongly against removing this function on mere
>>> proscriptive grounds and a deprecation is effectively removal for most
>>> users who care about warnings.
>> This strikes me as troubling. Are we considering deprecations to be
>> equivalent to removals, in terms of stability impact? I've heard more than
>> one person suggest that we are, or should. The argument for it is reasonably
>> clear: with -Werror enabled, as many people do, as many would encourage,
>> even, either removal or deprecation of something you use will break your
>> build.
>> But surely the *entire purpose* of deprecations is to be *less* damaging
>> than removals, and so if we're implicitly considering them equally bad, that
>> suggests to me that our deprecation mechanism is totally broken, and needs
>> to be fixed.
>> I can think of several potential fixes, but I'd first like to see if
>> others agree that there is a problem :)
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