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Today's Topics:
1. Re: Expose every Function of a wrapped type (Francesco Ariis)
----------------------------------------------------------------------
Message: 1
Date: Fri, 15 Nov 2019 15:11:12 +0100
From: Francesco Ariis <fa...@ariis.it>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] Expose every Function of a wrapped
type
Message-ID: <20191115141112.ga15...@x60s.casa>
Content-Type: text/plain; charset=iso-8859-1
Hello Leonardh,
a couple of ideas:
On Fri, Nov 15, 2019 at 11:36:03AM +0000, Leonhard Applis wrote:
> I currently have a newtype definition of a typed Data.Map.
>
> newtype G = G Data.Map String Values
>
> [...]
>
> However, if I have
>
> type G2 = Data.Map String Values
`Map k v` is already an instance of `Monoid` (when `v` is an instance
of `Ord`), are you sure you need to write another one? If the answer
is "yes", you can write a small helper:
withG :: (M.Map String a -> M.Map String a) -> G a -> G a
withG mf (G m) = G $ mf m
or use GeneralizedNewtypeDeriving to ease some pain:
{-# Language GeneralizedNewtypeDeriving #-}
module Prova where
import Data.Map as M
import GHC.Exts
newtype G a = G { unwrapG :: M.Map String a }
deriving (Eq, Show, Functor, Foldable)
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