是什么导致 cabal 中的这个模块 (NumberTheory) 安装错误？

Question

我在尝试为 Haskell

安装数论模块时遇到以下错误

PS C:\Users\prker\Desktop\Haskell SFs> cabal new-install NumberTheory -j1
Wrote tarball sdist to C:\Users\prker\Desktop\Haskell
SFs\dist-newstyle\sdist\Haskell-SFs-0.1.0.tar.gz
Resolving dependencies...
Build profile: -w ghc-8.6.5 -O1
In order, the following will be built (use -v for more details):
 - NumberTheory-0.1.0.1 (lib) (requires build)
Configuring library for NumberTheory-0.1.0.1..
Preprocessing library for NumberTheory-0.1.0.1..
Building library for NumberTheory-0.1.0.1..
[1 of 1] Compiling NumberTheory     ( NumberTheory.hs, dist\build\NumberTheory.o )

NumberTheory.hs:422:10: error:
    * Could not deduce (Semigroup (GaussInt a))
        arising from the superclasses of an instance declaration
      from the context: Monoid a
        bound by the instance declaration at NumberTheory.hs:422:10-42
    * In the instance declaration for `Monoid (GaussInt a)'
    |
422 | instance (Monoid a) => Monoid (GaussInt a) where
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Warning: Some package(s) failed to build. Try rerunning with -j1 if you can't
see the error.

这似乎是模块本身的语法错误，但这似乎不太可能。我已经尝试重新安装 cabal 并确保所有其他模块都是最新的。

Answer 1

基于information on Hackage the package was published in february 2016. At that time latest release of the base package was base-4.8.2.0. In that package, there is a Monoid typeclass：

class Monoid a where
        mempty  :: a
        -- ^ Identity of 'mappend'
        mappend :: a -> a -> a
        -- ^ An associative operation
        mconcat :: [a] -> a

但它因此不要求成员是 Semigroup 类型类的实例，事实上该类型类还不存在。

自 base-4.11.0.0 起，定义已更改为：

class <b>Semigroup a =></b> Monoid a where
        -- | Identity of 'mappend'
        mempty  :: a

        -- | An associative operation
        --
        -- __NOTE__: This method is redundant and has the default
        -- implementation @'mappend' = '(<>)'@ since /base-4.11.0.0/.
        mappend :: a -> a -> a
        mappend = (<>)
        {-# INLINE mappend #-}

        -- | Fold a list using the monoid.
        --
        -- For most types, the default definition for 'mconcat' will be
        -- used, but the function is included in the class definition so
        -- that an optimized version can be provided for specific types.
        mconcat :: [a] -> a
        mconcat = foldr mappend mempty

因此它要求属于 Monoid 类型类成员的类型也必须是 Semigroup type class 类型的成员。图书馆当然没有预料到这一点。

系统仍然打算编译它的原因是因为 NumberTheory 的 package description 说：

  build-depends:       <b>base ==4.*</b>, containers ==0.5.*, primes ==0.2.*

因此假设它可以使用版本 4.* 的任何版本的 base 构建软件，因此 4.11 及更高版本仍然被认为是很好的候选者。

是什么导致 cabal 中的这个模块 (NumberTheory) 安装错误？

What is causing this module (NumberTheory) installation error in cabal?

haskell

cabal