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Hope (programming language)

Hope is a small functional programming language developed in the 1970s at the University of Edinburgh.[1][2][3][4] It predates Miranda and Haskell and is contemporaneous with ML, also developed at the University. Hope was derived from NPL,[2] a simple functional language developed by Rod Burstall and John Darlington in their work on program transformation.[5] NPL was, in turn, derived from Kleene recursion equations. NPL and Hope are notable for being the first languages with call-by-pattern evaluation and algebraic data types.[citation needed] Hope is an important language in the development of functional programming.

Hope was named for Sir Thomas Hope (c. 1681–1771), a Scottish agricultural reformer, after whom Hope Park Square in Edinburgh, the location of the Department of Artificial Intelligence at the time of the development of Hope, was also named.

Language detailsEdit

A factorial program in Hope is:

dec fact : num -> num;
--- fact 0 <= 1;
--- fact n <= n*fact(n-1);

Unlike Haskell, changing the order of the clauses does not change the meaning of the program, because Hope's pattern matching always favors more specific patterns over less specific ones. Another way in which Hope differs from Haskell and ML is that explicit type declarations in Hope are required: there is no option to use a type-inference algorithm in Hope.

The first implementation of Hope was strict, but since that one there have been lazy versions and strict versions with lazy constructors (the language described in [1] has a lazy constructor for lists only). British Telecom embarked on a project with Imperial College to implement a strict version. The first release was coded by Thanos Vassilakis in 1986. Further releases were coded by Mark Tasng of BT.


  1. ^ a b Burstall R.M, MacQueen D.B, Sannella D.T. (1980) Hope: An Experimental Applicative Language. Conference Record of the 1980 LISP Conference, Stanford University, pp. 136-143.
  2. ^ a b R.M. Burstall. Design considerations for a functional programming language. Invited paper, Proc. Infotech State of the Art Conf. “The Software Revolution”, Copenhagen, 45–57 (1977)
  3. ^ Bailey, Roger (1 April 1990). Functional Programming with Hope. Ellis Horwood Series in Computers and Their Applications. Ellis Horwood Ltd. 
  4. ^ Bailey, Roger. "A Hope Tutorial". Byte. Vol. 10 no. 8 (August 1985). Retrieved 1 April 2015. 
  5. ^ R.M. Burstall and J. Darlington. A transformation system for developing recursive programs. Journal of the Association for Computing Machinery, 24(1):44–67 (1977)

External linksEdit