When it comes to Haskell, the elephant in the room is the Evil Mangler. It is no misnomer. To mangle code in order to accomplish a workaround or an optimization hack is no small evil. It goes against the modularity and reuse principle which is the core of Haskell philosophy. It is the wrong way to write a compiler, period. Just like C++ uses name-mangling, Haskell uses code-mangling. It is all evil. Haskell should have been bootstrapped from assembly on some high-speed computer and then used to port itself. It should never have been developed by means of kludgy hacks. It should have been a pure boot job, not a combination of Perl, C, and itself. So you believe in pure functional programming? I do too. And I also believe in pure bootstrapping.

Anyone who has done functional programming has probably encountered the function map. Something like map sq [1,2,3,4,5] computes to [1,4,9,16,25]. map is easy to write, but no one writes it oneself. Rather, map is a built-in function. My radical opinion is that map should never be built-in. It should be available in a library, but the library should exist as actual source code that would compile or run in that language. The library should not be mere object code that was compiled by another language.

map is easy to understand. It can be explained mathematically. One can easily get a handle on exactly what map does and use it with confidence. There are many good tutorials that include map in their examples of the power of functional programming. It should be the same with every level of abstraction from the simplest to the most complex. The documentation should always be available as open-source information. If the abstraction has a basis in a mathematical theory, that theory should be included in the documentation, so that anyone using the construct can understand and use it with confidence.

For example, you have probably seen list abstraction, which is similar to set abstraction. As a mathematician, I like set abstraction. As a programmer, I avoid list abstraction, unless I know how it is implemented in the language core.