Re: Proposal to deprecate and then drop fromJust

I'm a big fan of fromJust, so a -1 to this proposal. I'm also a fan of adding fromLeft and fromRight, but doubt anyone is going to agree with me. These functions have an obvious meaning, and an obvious implementation and an obvious name - they're handy. They should be used with caution, and documented as to their downsides, but they're still useful. I also wouldn't describe fromJust as "unsafe", merely that "using fromJust might be unsafe" - and that's something you might reasonably want to check (and could, with the Catch tool, http://community.haskell.org/~ndm/catch/, which is now thoroughly dead). As to the HLint warning, I'm not a great fan of it, since it's basically saying "use explicit error since your compiler won't give you a stack trace". I want to do configurable packages of HLint replacements, so having it in there is a reasonable thing. I'll think some more on that aspect. Thanks, Neil On Tue, Feb 24, 2015 at 1:09 PM, Oleg Grenrus wrote:

And I did it myself, as it was about adding one single line rule:

https://github.com/ndmitchell/hlint/pull/115

Let’s see what Neil thinks about :)

- Oleg

On 24 Feb 2015, at 12:28, Oleg Grenrus wrote:

On 24 Feb 2015, at 12:23, Erik de Castro Lopo wrote:

Possibly what we need is a pragma to mark functions partial and a warning flag that warns on usage of functions that have been marked partial.

I had this in mind too, but that is very heavy solution. I’d rather start with making hlint warnings?

foo :: Maybe Int -> Int foo x = if isJust x then fromJust x else 0

bar :: Maybe Int -> Int bar x = 1 + fromJust x

It warns about `foo` nonsense. It could propose to change `bar` part into `fromMaybe (error “I’know what I’m doing”) x` ?

- Oleg

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