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A class for types with a default value

Haskell 84.69% Makefile 15.31%

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sol dag jaspervdj jfischoff 2piix wdanilo abbradar hvr ryantrinkle vwwv matsubara0507 mitchellwrosen treeowl hapytex sysfce2

data-default's Issues

Remove most instances

My opinion: def is a useful concept for blobs of optional parameters, configs, and perhaps other domain-specific things, but not for numeric types, lists, Maybe, etc.

The situation today is, from my vantage point: either people avoid this type class entirely (e.g. google/proto-lens#194), or they use it with some caveats like, try not to abuse it.

I propose we try to correct this by making a major version bump to 2.0 and removing most instances. The only ones I believe belong are the derived tuple instances like

instance (Default a, Default b) => Default (a, b)

What do you think? Is this a feasible or wanted change? Thanks :)

DefaultSignatures extension can be used to make Monoid default

{-# LANGUAGE DefaultSignatures #-}

import Data.Monoid
class Default a where
    def :: a
    default def :: Monoid a => a
    def = mempty

stack build tools support

Please refresh your library dependencies to become compatible with stack tools. It guess it should compiles with latest versions of cabal packages

Add GDefault instance for (a :+: b)

The usefulness of the Default class came from its ability to generically derive Default instances. I would argue that adding a GDefault instance for sum types (which selects the first constructor) would further boost its usefulness. Plus we lose nothing from adding this since right now we need to manually write Default instances for sum types anyways.

Is Default (e -> r) necessary?

Do you personally use the (e -> r) instance? Do you know if anybody else does? I'm trying to define:

data Preference = Preference 
  { userId :: UserId
  , max   :: Int
  }

Obviously, the UserId can't be defaulted (sensibly -- i.e., while respecting the app's semantics for a UserId), but it would be pretty nice to be able to define:

instance Default (UserId -> Preference) where
  def = \uid -> (Preference uid 1000)

Default for `Proxy`

It would be useful to have a default for Proxy

instance Default (Proxy a) where def = Proxy

Add to stackage

Hello, this library looks really good to me and i would like to use it in my haskell stack project. Could it be added to stackage ?

Merge packages data-default-class and data-default-instances-base

I may be missing something, but as I see it the reason to split the original data-default into separate packages is to minimize dependencies.

As both data-default-class and data-default-instances-base only introduce the base dependency, we could merge the packages.

Keeping the separate packages has the downside that the instances in data-default-instances-base are orphan (which I generally considered undesirable). Are there any upsides?

Drop the instance for function

The current instance isn't very useful and it occupies the space for a whole universe of way more useful default morphism instances, e.g.:

instance Default (Int8 -> Int) where def = fromIntegral
instance Default (String -> Data.Text.Text) where def = Data.Text.pack

Basically, the whole "conversion" ecosystem could be encoded this way.

Add Default instance for Bool

Currently it's missing. Should return False.

data-default-class-0.1.0 is missing GHC.Generics support for GHC 7.4

This has the unfortunate effect of violating the PVP contract, as data-default-class-0.1.0 lacks Generics support for GHC 7.4 even though GHC 7.4 does support Generics and will result in hard to fix install-plan issues on Hackage if left un-addressed.

My recommendation is to quickly release data-default-class-0.1.0.1 providing Generics support for GHC 7.4. I can provide a PR if needed.

Release new version on Hackage

It would be nice to have new version released with Generics support.