Features of Curry

To get an idea of the multi-paradigm programming language Curry, 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)

These are the basic features of the kernel language. Look into the Curry report if you are interested in more details. Further features might be added in different extensions of this kernel language.