The default libraries are extremely inefficient.

Generally if I use Python/Ruby I can get a 50x slow down that is accepted, but with Haskell it can be more, as it's very hard to think about what the compiler does (memory usage can blow up easily).

(Also the fibonacci sequence using 'zip'. Blew my mind.)

Haskell folks are fairly upfront about possible performance issues. Lazy evaluation comes with its own set of tradeoffs.

You can write very inefficient code in C++ if your algorithm isn't efficient.

,,The purity of Haskell code makes it easy to fuse chains of functions together, allowing for performance benefits.’’

Having something ,,beautiful’’ and inefficient is the problem I’m writing about. The language itself is guiding people to inefficiency.

I haven’t felt this with C++, so I’m not sure what you are talking about: usually simple / pretty code runs fast there, and more complex code runs slower.