{{Infobox programming language
, name = Escher
, logo =
, paradigm = declarative:
functional
Functional may refer to:
* Movements in architecture:
** Functionalism (architecture)
** Form follows function
* Functional group, combination of atoms within molecules
* Medical conditions without currently visible organic basis:
** Functional s ...
,
logic
Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premis ...
static
Static may refer to:
Places
*Static Nunatak, a nunatak in Antarctica
United States
* Static, Kentucky and Tennessee
*Static Peak, a mountain in Wyoming
** Static Peak Divide, a mountain pass near the peak
Science and technology Physics
*Static e ...
,
manifest
Manifest may refer to:
Computing
* Manifest file, a metadata file that enumerates files in a program or package
* Manifest (CLI), a metadata text file for CLI assemblies
Events
* Manifest (convention), a defunct anime festival in Melbourne, Aus ...
simple theory of types The type theory was initially created to avoid paradoxes in a variety of formal logics and rewrite systems. Later, type theory referred to a class of formal systems, some of which can serve as alternatives to naive set theory as a foundation for a ...
M. C. Escher
Maurits Cornelis Escher (; 17 June 1898 – 27 March 1972) was a Dutch graphic artist who made mathematically inspired woodcuts, lithographs, and mezzotints.
Despite wide popular interest, Escher was for most of his life neglected in th ...
programming language
A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language.
The description of a programming l ...
that supports both
functional programming
In computer science, functional programming is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions that ...
and
logic programming
Logic programming is a programming paradigm which is largely based on formal logic
Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of log ...
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
Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premises i ...
, and the program's execution (computation) is a deduction from the theory. The logic framework for Escher is
Alonzo Church
Alonzo Church (June 14, 1903 – August 11, 1995) was an American mathematician, computer scientist, logician, philosopher, professor and editor who made major contributions to mathematical logic and the foundations of theoretical computer scie ...
's
simple theory of types The type theory was initially created to avoid paradoxes in a variety of formal logics and rewrite systems. Later, type theory referred to a class of formal systems, some of which can serve as alternatives to naive set theory as a foundation for a ...
.
Escher, notably, supports I/O through a monadic type representing the 'outside world', in the style of
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 has pioneered a number of programming lan ...
.
One of the goals of Escher's designers was to support
meta-programming
Metaprogramming is a programming technique in which computer programs have the ability to treat other programs as their data. It means that a program can be designed to read, generate, analyze or transform other programs, and even modify itself ...
, and so the language has comprehensive support for generating and transforming programs.
Examples
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 1,r2 (r = LAMBDA (SOME (r1(Fst(u),z) & r2(z,Snd(u)))) &
PrimitiveRel(r1) & PrimitiveRel(r2))).