What does the /= operator in Haskell mean?
It means not equal. So 5 /= 5 is false as 5 == 5 is true. x /= y = not (x == y) As suggested, it recalls the mathematical symbol “≠” (/=) opposite to “=” (==).
haskell
Subsumption in polymorphic types
The typechecker doesn’t know when to apply the subsumption rule. You can tell it when with the following function. Prelude> let u :: ((f a -> f a) -> c) -> ((forall b. f b -> f b) -> c); u f n = f n This says, given a function from a transformation for … Read more
Monad transformers libraries – which one to use? [closed]
The Haskell Platform specifies mtl and transformers as standard. If you’re unsure, you should just use mtl. However, if you have a specific technical reason to look at the new libraries, they tend to address issues or add new features to mtl. monadLib in particular has some new features.
Haskell library like SymPy? [closed]
Please check out the numbers package. If all you need is to store exact numbers like “1 + √3”, you may want to use Data.Number.CReal instead of symbolic arithmetics. It stores the expressions and can be computed to arbitrary number of digits when needed. Prelude Data.Number.CReal> let cx = 1 + sqrt (3 :: CReal) … Read more
What is the difference between `ix` and `at` in the Lens library of Haskell
That at and ix are different is already noticable if you look at the available instances for the classes containing these functions: instances of At: Map, IntMap, HashMap instances of Ixed: [a], Map, ByteString, Text, and a lot more All instances if At are also an instance of Ix, but not all instances of Ix … Read more
What IO activity does the GHC IO manager support?
Any file descriptor that can be managed by epoll/kqueue is eligible. Libraries that want asynchronous treatment of I/O need to cooperate with the I/O manager by making file descriptors non-blocking, and calling the threadWaitRead and threadWaitWrite functions in GHC.Conc before retrying a system call that previously returned EWOULDBLOCK. This has already been done for the … Read more
Haskell: Suppress quotes around strings when shown
Firstly, take a look at this question. Maybe you will be satisfied with toString function. Secondly, show is a function that maps some value to a String. So, it makes sense that quotes should be escaped: > show “string” “\”string\”” Is there a function that works like f that I’ve described above? Seems like you’re … Read more
Is Haskell suitable for quantum computing?
Haskell has been used as a quantum programming language for a while now. The primary point of reference would be the Quipper DSL in Haskell. Quipper paper New Scientist article on Quipper And more fun stuff – http://www.kurzweilai.net/quipper-language-makes-quantum-computers-easier-to-program
How can two continuations cancel each other out?
A function f :: a -> b can be “disguised” inside double continuations as a function f’ :: ((a -> r1) -> r2) -> ((b -> r1) -> r2). obfuscate :: (a -> b) -> ((a -> r1) -> r2) -> (b -> r1) -> r2 obfuscate f k2 k1 = k2 (k1 . f) … Read more
When choosing a functional programming language for use with LLVM, what are the trade-offs?
Either OCaml or Haskell would be a good choice. Why not check out the LLVM tutorials for each language? The LLVM tutorial for OCaml is here: http://llvm.org/docs/tutorial/OCamlLangImpl1.html Haskell has more momentum these days, but there are plenty of good parsing libraries for OCaml as well including the PEG parser generator Aurochs, Menhir, and the GLR … Read more