小编Ste*_*ill的帖子

我在股票64位Ubuntu 15:10上安装了mariadb-10.1.

我成功安装了libmysqlclient18,但在尝试安装libmysqlclient-dev时遇到错误.

steve@steve:~$ dpkg -s libmysqlclient18
Package: libmysqlclient18
Status: install ok installed
Priority: optional
Section: libs
Installed-Size: 10
Maintainer: MariaDB Developers <maria-developers@lists.launchpad.net>
Architecture: amd64
Source: mariadb-10.1
Version: 10.1.13+maria-1~wily
Replaces: libmysqlclient18 (<< 10.1.13+maria-1~wily)
Depends: libmariadbclient18 (= 10.1.13+maria-1~wily)
Description: Virtual package to satisfy external depends
 This is an empty package that provides an updated "best" version of
 libmysqlclient18 that does not conflict with the libmariadbclient18
 package.
 .
 MariaDB is a fast, stable and true multi-user, multi-threaded SQL database
 server. SQL (Structured …

我有这个 Haskell 代码片段：

{-# LANGUAGE InstanceSigs #-}\n\nmodule LatticePoint \nwhere\n\nimport Data.List    \n\ndata (Eq v) => LatticePoint v = LatticePoint{prob::Double, value::v}\n\ninstance Functor LatticePoint where\n    fmap :: (Eq a, Eq b) => (a -> b) -> LatticePoint a -> LatticePoint b \n    fmap f lp = LatticePoint {prob = prob lp, value = f $ value lp}\n

编译时出现以下错误，我不明白

src/LatticePoint.hs:12:14: error:\n    \xe2\x80\xa2 No instance for (Eq a)\n      Possible fix:\n        add (Eq a) to the context of\n          the type signature for:\n            fmap …