Escher (programming language)
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| Paradigm | declarative: functional, logic |
|---|---|
| Designed by | J.W. Lloyd |
| First appeared | mid-1990s |
| Typing discipline | static, manifest |
| Major implementations | |
| Kee Siong Ng's implementation | |
| Influenced by | |
| simple theory of types | |
Escher (named for M. C. Escher, "a master of endless loops") is a declarative programming language that supports both functional programming and logic programming models, developed by J.W. Lloyd in the mid-1990s. It was designed mostly as a research and teaching vehicle. The basic view of programming exhibited by Escher and related languages is that a program is a representation of a theory in some logic framework, and the program's execution (computation) is a deduction from the theory. The logic framework for Escher is Alonzo Church's simple theory of types.
Escher, notably, supports I/O through a monadic type representing the 'outside world', in the style of Haskell. One of the goals of Escher's designers was to support meta-programming, and so the language has comprehensive support for generating and transforming programs.
Examples[edit]
MODULE Lambda. CONSTRUCT Person/0. FUNCTION Jane, Mary, John: One -> Person. FUNCTION Mother : Person * Person -> Boolean. Mother(x,y) => x=Jane & y=Mary. FUNCTION Wife : Person * Person -> Boolean. Wife(x,y) => x=John & y=Jane. FUNCTION PrimitiveRel : (Person * Person -> Boolean) -> Boolean. PrimitiveRel(r) => r=Mother \/ r=Wife. FUNCTION Rel : (Person * Person -> Boolean) -> Boolean. Rel(r) => PrimitiveRel(r) \/ (SOME [r1,r2] (r = LAMBDA [u] (SOME [z] (r1(Fst(u),z) & r2(z,Snd(u)))) & PrimitiveRel(r1) & PrimitiveRel(r2))). References[edit]
- Declarative programming in Escher, JW Lloyd, University of Bristol, Bristol, UK, 1995
- An implementation of Escher (Some dead links can be reached from the archived page (or by substituting the new domain in the link in question).)