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Curry

Language type:

F - Functional or lambda-based

Description:

Curry is a fairly recent functional logic programming language, developed as a research vehicle to test ideas in the areas of narrowing, unification, and non-determinism. It has also been used to teach logic and functional programming principles.

The syntax of Curry is complex, compact, and similar to that of Haskell. Each statement of a Curry program is an equation or predicate. Executing a Curry program consists of simplifying equations and expressions until a particular specified goal is reached or a particular solution is obtained. Primitive data types supported by Curry include booleans, integers, reals, chars, and strings. Aggregate and specialized data types include tuples, lists, functions, and constraints. Oddly enough, Curry uses the same comment syntax as Ada. The module construct serves to encapsulate libraries of functions, data types, and expressions. The module seems to be the only program structuring facility in Curry.

Like many functional languages, Curry supports a declarative I/O model. This kind of model basically represents input and output operations as expressions involving 'the World'.

Some of the advanced features of Curry are listed below.

• Functional composition
• Predicate constraints
• Nested Expressions
• Higher-order functions
• Concurrency
• Lazy evaluation
• residuation
• Narrowing

Curry can also call external functions, which offers a way to support the advanced logical model with more traditional programming.

As an academic project, implementations of Curry are available free. Documentation is available on the web, but almost exclusively in DVI format.

Origin:

Michael Hanus,RWTH Aachen, Germany, 1997

See Also:

Haskell    LEDA    Prolog    Goedel    SML   

Remarks:

The current version of the Curry language seems to be 0.5. The language is still under development, but the most recent version of the language manual is dated 1/99, so the development may have stalled.

Several implementations of Curry exist. The most viable one seems to be PACS, the Portland Aachen Curry System. It is a compiler that translates Curry programs into various intermediate forms: Prolog or Java. Free downloads of PACS for UNIX systems are available from RWTH Aachen. Other Curry implementations are interpreters written in Prolog.

There has been a trend in the 1990s to try to integrate ideas from some of the most powerful computer programming research paradigms. Curry, like LEDA and NIAL, is an example of this trend.

Links:

Features of Curry

TasteCurry WWW interpreter

Date:

Last updated 8/8/99

Sample code:

This is a sorting example from the TasteCurry WWW Curry interface.

-- quicksort using higher-order functions:

-- filter elements in a list (predefined as `filter'):
filter_ :: (a -> Bool) -> [a] -> [a];
filter_ _ []     = []
filter_ p (x:xs) = if p x then x : filter_ p xs
                          else filter_ p xs

qsort :: [Int] -> [Int]
qsort []     = []
qsort (x:l)  = qsort (filter (< x) l)    x : qsort (filter (>= x) l)

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