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H

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

Hope

Language type:

F - Functional or lambda-based

Description:

Hope is a small, simple functional language based function composition and on the idea of 'call-by-pattern.' A Hope program consists of a set of modules, each of which can contain sets of recursion equations. Current implementations of Hope use full lazy evaluation. Unlike some of the original functional languages, Hope is strongly typed.
There were a couple of dialects of Hope, corresponding to different groups' implementations. The one that seems available today was originally called Hope .
Data types supported by Hope include numbers, symbols, strings, lists, and tuples. (Constituents of a list must be all the same type, while tuples can be heterogenous.) A Hope programmer can define their own primitive and aggregate types. This ability to create true abstract data types is a novel feature in functional languages. Modern implementations of Hope use lazy evaluation.
A free implementation of the Hope interpreter is available for MS-DOS, Unix, and Macintosh.

Origin:

Burstall 1978, Perry, Kewley et al 1985.

See Also:

FP    ML    Clean    Haskell    Mathematica   

Remarks:

Hope was apparently the first functional language to employ argument/return pattern-matching as a polymorphism semantic. This kind of approach is carried on today in some symbolic programming systems, notably Mathematica, as well as many newer functional languages.
The original language Hope was developed at Edinburgh U. by Burstall in the late 1970s. A successor, called Hope , was developed at ICL by J. Kewley, T. Thomson, and others in the mid-1980s; the first implementation used eager evaluation, but later ones switch to the more advanced lazy evaluation strategy.

Links:

Hope code examples

Date:

Last updated 1/4/2000

Sample code:

A module for listing the contents of a tree by breadth-first traversal using lazy evaluation, from Ross Paterson's Hope web page.

use lists, functions, products;

type rose_tree alpha == alpha # list(rose_tree alpha);

  dec bf_list : rose_tree alpha -> list alpha;
     --- bf_list t <= [t].
             iterate (concat o map snd).
             front_with (/= []).
             concat.
             map fst;

HyperTalk

Language type:

C - Command or Scripting

Description:

HyperTalk is the scripting language for Apple's information presentation system HyperCard. It has a simple and English-like syntax, a modest set of general and application-specific data types, and the usual procedural control structures. HyperTalk was designed to allow HyperCard information collections, which are called "stacks", to be more dynamic and interactive. Because Apple envisioned the users of HyperTalk to be multimedia developers and not traditional programmers, they HyperTalk interpreter was designed to be very forgiving: it allows various syntactic sugar, type conversion is automatic, and everything is case-insensitive.
Most of a HyperTalk program will often consist of handers, subroutines to be called when the end-user performs some action or when a certain condition obtains. HyperTalk supports the notion of add-on 'external' functions and commands; these are roughly analogous to library modules in a language like C.
HyperCard 2 compiles individual HyperTalk functions into intermediate codes the first time the function is called. This is done to reduce start-up time for HyperCard applications.
There are several versions of HyperTalk. The two main versions from Apple correspond to HyperCard releases 1 and 2. Aldus SuperCard supports a superset of HyperTalk called SuperTalk. Commercial implementations of both are available for the Macintosh. At one time, SuperCard was also available for MS-Windows, but that may not be true anymore.

Origin:

Atkinson and Winkler, Apple Computer, 1986?

See Also:

Lingo    AppleScript   

Remarks:

HyperTalk continues to evolve along with the HyperCard product (version 3 due soon), but it is unclear whether it is still going to be a viable language. Apple is touting AppleScript as THE scripting language for all Macintosh applications, so HyperTalk may be superseded.
HyperTalk was very influential on the niche area of multimedia scripting languages. For example, the scripting language used by the current (c. 1997) market leader in multimedia authorware resembles HyperTalk in many respects.

Links:

Hypercard FAQ Page

Hypercard Heaven

Date:

Last updated 12/7/97

3 entries retrieved.

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