Hope is a

programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...

based on

functional programming In computer science, functional programming is a programming paradigm where programs are constructed by Function application, applying and Function composition (computer science), composing Function (computer science), functions. It is a declarat ...

developed in the 1970s at the

University of Edinburgh The University of Edinburgh (, ; abbreviated as ''Edin.'' in Post-nominal letters, post-nominals) is a Public university, public research university based in Edinburgh, Scotland. Founded by the City of Edinburgh Council, town council under th ...

. It predates Miranda and

Haskell Haskell () is a general-purpose, statically typed, purely functional programming language with type inference and lazy evaluation. Designed for teaching, research, and industrial applications, Haskell pioneered several programming language ...

and is contemporaneous with ML, also developed at the University. Hope was derived from NPL, a simple functional language developed by Rod Burstall and John Darlington in their work on program transformation. NPL and Hope are notable for being the first languages with call-by-pattern evaluation and

algebraic data type In computer programming, especially functional programming and type theory, an algebraic data type (ADT) is a kind of composite data type, i.e., a data type formed by combining other types. Two common classes of algebraic types are product ty ...

s. Hope was named for Sir Thomas Hope (c. 1681–1771), a Scottish

agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...

reformer, after whom ''Hope Park Square'' in

Edinburgh Edinburgh is the capital city of Scotland and one of its 32 Council areas of Scotland, council areas. The city is located in southeast Scotland and is bounded to the north by the Firth of Forth and to the south by the Pentland Hills. Edinburgh ...

, the location of the

artificial intelligence Artificial intelligence (AI) is the capability of computer, computational systems to perform tasks typically associated with human intelligence, such as learning, reasoning, problem-solving, perception, and decision-making. It is a field of re ...

department at the time of the development of Hope, was also named. The first implementation of Hope used strict evaluation, but there have since been

lazy evaluation In programming language theory, lazy evaluation, or call-by-need, is an evaluation strategy which delays the evaluation of an Expression (computer science), expression until its value is needed (non-strict evaluation) and which avoids repeated eva ...

versions and strict versions with lazy constructors. A successor language Hope+, developed jointly between Imperial College and

International Computers Limited International Computers Limited (ICL) was a British computer hardware, computer software and computer services company that operated from 1968 until 2002. It was formed through a merger of International Computers and Tabulators (ICT), English Ele ...

, added annotations to dictate either strict or lazy evaluation.

Language details

factorial In mathematics, the factorial of a non-negative denoted is the Product (mathematics), product of all positive integers less than or equal The factorial also equals the product of n with the next smaller factorial: \begin n! &= n \times ...

program in Hope is: dec fact : num -> num; --- fact 0 <= 1; --- fact n <= n*fact(n-1); Changing the order of clauses does not change the meaning of the program, because Hope's pattern matching always favors more specific patterns over less specific ones. Explicit declarations of

data type In computer science and computer programming, a data type (or simply type) is a collection or grouping of data values, usually specified by a set of possible values, a set of allowed operations on these values, and/or a representation of these ...

s in Hope are required; there is no

type inference Type inference, sometimes called type reconstruction, refers to the automatic detection of the type of an expression in a formal language. These include programming languages and mathematical type systems, but also natural languages in some bran ...

algorithm. Hope provides two built-in

data structure In computer science, a data structure is a data organization and storage format that is usually chosen for Efficiency, efficient Data access, access to data. More precisely, a data structure is a collection of data values, the relationships amo ...

tuple In mathematics, a tuple is a finite sequence or ''ordered list'' of numbers or, more generally, mathematical objects, which are called the ''elements'' of the tuple. An -tuple is a tuple of elements, where is a non-negative integer. There is o ...

s and lists.

Implementations

Roger Bailey's Hope tutorial in the August 1985 issue of ''

Byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...

'' references an interpreter for IBM PC DOS 2.0. British Telecom embarked on a project with

Imperial College London Imperial College London, also known as Imperial, is a Public university, public research university in London, England. Its history began with Prince Albert of Saxe-Coburg and Gotha, Prince Albert, husband of Queen Victoria, who envisioned a Al ...

to implement a version of Hope. The first release was coded by Thanos Vassilakis in 1986. Further releases were coded by Mark Tasng of British Telecom.

References

External links

Hope Interpreter for WindowsEntry in the online Dictionary of Programming Languages
{{DEFAULTSORT:Hope (Programming Language) Functional languages Academic programming languages History of computing in the United Kingdom Statically typed programming languages University of Edinburgh Articles with example code