:reload (or :r) reloads everything in ghci: Prelude> :l helloworld.hs It comes shipped with most Haskell environments, such as ghci which comes with the GHC compiler: ghci> putStrLn "Hello World!"Īlternatively, load scripts into ghci from a file using load (or :l): ghci> :load helloworld The interactive REPL can also be used instead of compiling. helloworldĪlternatively, runhaskell or runghc make it possible to run the program in interpreted mode without having to compile it: runhaskell helloworld.hs Put this into a helloworld.hs file and compile it using a Haskell compiler, such as GHC: ghc helloworld.hsĮxecuting the compiled file will result in the output "Hello, World!" being printed to the screen. This type annotation is usually omitted for main because it is its only possible type. The first line is an optional type annotation, indicating that main is a value of type IO (), representing an I/O action which "computes" a value of type () (read "unit" the empty tuple conveying no information) besides performing some side effects on the outside world (here, printing a string at the terminal). VersionsĪ basic "Hello, World!" program in Haskell can be expressed concisely in just one or two lines: main :: IO () Great place to find books, courses, tutorials, manuals, guides, etc. The official Haskell documentation is also a comprehensive and useful resource. As of May 2016, a group is working on the next version, Haskell 2020. The latest standard of Haskell is Haskell 2010. Packages: Open source contribution to Haskell is very active with a wide range of packages available on the public package servers.General-purpose: Haskell is built to be used in all contexts and environments.
Delays the evaluation of an expression until its value is needed. Lazy evaluation: Functions don't evaluate their arguments.Concurrent: Its flagship compiler, GHC, comes with a high-performance parallel garbage collector and light-weight concurrency library containing a number of useful concurrency primitives and abstractions.There are no statements or instructions, only expressions which cannot mutate variables (local or global) nor access state like time or random numbers. Purely functional: Every function in Haskell is a function in the mathematical sense.If a program passes a static type checker, then the program is guaranteed to satisfy some set of type safety properties for all possible inputs. Static type checking is the process of verifying the type safety of a program based on analysis of a program's text (source code). Statically typed: Every expression in Haskell has a type which is determined at compile time.Haskell is an advanced purely-functional programming language. Common functors as the base of cofree comonads.Arbitrary-rank polymorphism with RankNTypes.show) (writeBrewfile >=> \_ -> putStrLn "Brewfile generated!") all getInstalledApps :: IO getInstalledApps = do filePaths filePaths pure $ Cask names fetchInstallableAppsWithBrew :: IO fetchInstallableAppsWithBrew = runReq defaultHttpConfig $ do res unNames ( Response xs) = unName xs where unName :: Package -> String unName ( Package name) = head name getBrewDumpLines :: IO ( Either ParseError ) getBrewDumpLines = do out IO () writeBrewfile = writeFile "Brewfile". : "name" data BrewfileLine = Tap String | Brew String | Cask String deriving ( Eq) instance Show BrewfileLine where show ( Tap s) = "tap \"" s "\"" show ( Brew s) = "brew \"" s "\"" show ( Cask s) = "cask \"" s "\"" instance Ord BrewfileLine where ( lines either (die. #!/usr/bin/env stack deriving ( Generic, Show, ToJSON) instance FromJSON Package where parseJSON = withObject "Package" $ \v -> Package v.