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Haskell

Language type:

F - Functional or lambda-based

Description:

Haskell is a non-strict purely functional language, usually interpreted, designed by representatives of the functional programming community. The motivation for Haskell was unification of functional programming through the introduction of a standard, widespread, modern language.
Haskell is a strongly typed language with a rich type system. As in all functional language, computations are performed only by expressions; every expression has a type. Primitive data types supplied by the language include: integers, reals, characters, lists, enumerations, tuples, and various function mappings. Haskell language implementations perform static type checking prior to execution.
Haskell functions are defined as mappings between parts of the type space. Of course, composition, curried functions, lambda forms, and higher-order functions are supported. Haskell uses lazy evaluation. It also permits definition of operators as functions (operator overloading), a convenience feature that is unusual in functional programming systems.
Modularity is explicitly supported by Haskell. Programs consist of named modules. The module facility provides distinct namespaces and a means for defining encapsulated abstract data types. Haskell's module features allow some degree of object oriented programming.
The Haskell standard library is written using the module facility. It provides additional numeric data types, various standard aggregate types like arrays and lists, system interface and I/O facilities, time and date handling, and random number generation.
Several free academic implementations of Haskell are available, and good documentation is available at the main Haskell web site.

Origin:

Haskell Committee (Hughes, Wadler, Peterson et al), 1990.

See Also:

FP    Miranda    Clean    ML    Gofer   

Remarks:

The language is named after Haskell B. Curry, a logician and mathematician who worked on function theory; many ideas in functional programming originated with Curry (including the notion of curried functions).
Two main Haskell implementations, Glasgow Haskell Compiler (GHC) and Yale/Nottingham Hugs are based on C. GHC is a Haskell->C translator, and Hugs is an interpreter coded in C.
As of the end of 1997, the current version of the Haskell language definition was 1.4. A revised language definition, to be called Standard Haskell, should be finalized in 1998.

Links:

The Haskell 1.4 Language Report

main Haskell site in Europe

Haskell download area at Chalmers

Introduction to Functional Programming using Haskell

Date:

Last updated 12/21/97

Sample code:

-- Stable quicksort in Haskell by Lennart Augustsson
-- 

module QSort(sortLe, sort) where

sortLe :: (a -> a -> Bool) -> [a] -> [a]
sortLe le l = qsort le   l []

sort :: (Ord a) => [a] -> [a]
sort      l = qsort (<=) l []

-- qsort is stable and does not concatenate.
qsort le []     r = r
qsort le [x]    r = x:r
qsort le (x:xs) r = qpart le x xs [] [] r

-- qpart partitions and sorts the sublists
qpart le x [] rlt rge r =
    -- rlt and rge are in reverse order and must be sorted with an
    -- anti-stable sorting
    rqsort le rlt (x:rqsort le rge r)
qpart le x (y:ys) rlt rge r =
    if le x y then
        qpart le x ys rlt (y:rge) r
    else
        qpart le x ys (y:rlt) rge r

Descriptions in this dictionary are ©1997-99 Neal Ziring. Some examples copyright of their respective authors. Some technologies and languages are trademarked. Permission to copy descriptions is granted as long as authorship credit is preserved.

Comments on this dictionary, corrections and suggestions, are all welcome. Please use email, the address is ziring@home.com