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In Haskell, the code example filter even [ 1 .. 10 ] evaluates to the list 2, 4, …, 10 by applying the predicate even to every element of the list of integers 1, 2, …, 10 in that order and creating a new list of those elements for which the predicate returns the Boolean value true, thereby giving a list containing only the even members of ...
For example, digit parses a digit, and string parses a specific string (like "hello"). Parser combinator libraries like Parsec provide utility functions to run the parsers on real values. A parser to recognize a single digit from a string can be split into two functions: one to create the parser, and a main function that calls one of these ...
In Haskell, the polymorphic function map :: (a -> b) -> [a] -> [b] is generalized to a polytypic function fmap :: Functor f => (a -> b) -> f a -> f b, which applies to any type belonging the Functor type class. The type constructor of lists [] can be defined as an instance of the Functor type class using the map function from the previous example:
Much of Haskell code is similar to standard mathematical notation in facility and syntax. The first line of the factorial function describes the type of this function; while it is optional, it is considered to be good style [1] to include it. It can be read as the function factorial (factorial) has type (::) from integer to integer (Integer ...
Folds can be regarded as consistently replacing the structural components of a data structure with functions and values. Lists, for example, are built up in many functional languages from two primitives: any list is either an empty list, commonly called nil ([]), or is constructed by prefixing an element in front of another list, creating what is called a cons node ( Cons(X1,Cons(X2,Cons ...
A simple example (in Haskell) is a program which computes the sum of a list of numbers. We can define the sum function recursively using a pointed style (cf. value -level programming ) as: sum ( x : xs ) = x + sum xs sum [] = 0
Pages in category "Articles with example Haskell code" The following 56 pages are in this category, out of 56 total. This list may not reflect recent changes .
Hugs deviates from the Haskell 98 specification [2] in several minor ways. [3] For example, Hugs does not support mutually recursive modules. A list of differences exists. [4] The Hugs prompt is a Haskell read–eval–print loop (REPL). It accepts expressions for evaluation, but not module, type, or function definitions.