Features of Curry
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To get an idea of the multi-paradigm programming language
here is an (incomplete) list of its features:
Program entities: functions defined by equations (predicates are considered as Boolean functions or constraints)
Syntax: almost similar to Haskell
. In addition, declarations of free variables are allowed and program rules might overlap (leading to nondeterministic computations).
Type system: parametric polymorphism (a la Hindley/Milner)
Operational semantics: Basically, lazy reduction of functional expressions. However, function calls may contain free (logic) variables. Such function calls may be suspended (until the variable become instantiated by solving some predicate) or may be evaluated by non-deterministic instantiation of the variable, i.e., this operational semantics combines the ideas of “residuation” and “narrowing”. This operational semantics was firstly described in a POPL'97 paper
and another detailed description can be found in the Curry report
Higher-order functions; function application is delayed if functions are unknown (i.e., free variables).
Declarative (monadic) I/O
(Equational) constraints, concurrent evaluation of constraints
Encapsulated search to control the exploration of the search space (based on this feature, several predefined search strategies like depth-first search, breadth-first search, best solution search etc. are available)
Interface to constraint solvers and foreign functions
These are the basic features of the kernel language. Look into the
if you are interested in more details.
Further features might
be added in different extensions of this kernel language.