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While most Perl one-liners are imperative, Perl's support for anonymous functions, closures, map, filter (grep) and fold (List::Util::reduce) allows the creation of 'functional' one-liners. This one-liner creates a function that can be used to return a list of primes up to the value of the first parameter:
In languages which support first-class functions and currying, map may be partially applied to lift a function that works on only one value to an element-wise equivalent that works on an entire container; for example, map square is a Haskell function which squares each element of a list.
List comprehension is a syntactic construct available in some programming languages for creating a list based on existing lists. It follows the form of the mathematical set-builder notation (set comprehension) as distinct from the use of map and filter functions.
Filter is a standard function for many programming languages, e.g., Haskell, [1] OCaml, [2] Standard ML, [3] or Erlang. [4] Common Lisp provides the functions remove-if and remove-if-not. [5] Scheme Requests for Implementation (SRFI) 1 provides an implementation of filter for the language Scheme. [6]
Notice that the type of the result can be regarded as everything past the first supplied argument. This is a consequence of currying, which is made possible by Haskell's support for first-class functions; this function requires two inputs where one argument is supplied and the function is "curried" to produce a function for the argument not supplied.
The first revision, named Haskell 2010, was announced in November 2009 [2] and published in July 2010. Haskell 2010 is an incremental update to the language, mostly incorporating several well-used and uncontroversial features previously enabled via compiler-specific flags. Hierarchical module names.
As another example, the list of all Fibonacci numbers can be written in the programming language Haskell as: [13] fibs = 0 : 1 : zipWith ( + ) fibs ( tail fibs ) In Haskell syntax, " : " prepends an element to a list, tail returns a list without its first element, and zipWith uses a specified function (in this case addition) to combine ...
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 ...