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Lambda abstractions applied to a parameter have a dual interpretation as either a let expression defining a function, or as defining an anonymous function. Both interpretations are valid. These two predicates are needed for both definitions. lambda-free - An expression containing no lambda abstractions. {- [.
The term closure is often used as a synonym for anonymous function, though strictly, an anonymous function is a function literal without a name, while a closure is an instance of a function, a value, whose non-local variables have been bound either to values or to storage locations (depending on the language; see the lexical environment section below).
An example is the compareTo method: a. compareTo (b) checks whether a comes before or after b in some ordering, but the way to compare, say, two rational numbers will be different from the way to compare two strings. Other common examples of binary methods include equality tests, arithmetic operations, and set operations like subset and union.
In object-oriented programming, a covariant return type of a method is one that can be replaced by a "narrower" (derived) type when the method is overridden in a subclass. A notable language in which this is a fairly common paradigm is C++. C# supports return type covariance as of version 9.0. [1]
In this case particular lambda terms (which define functions) are considered as values. "Running" (beta reducing) the fixed-point combinator on the encoding gives a lambda term for the result which may then be interpreted as fixed-point value. Alternately, a function may be considered as a lambda term defined purely in lambda calculus.
In Julia, methods are associated with types, so it is possible to make any arbitrary Julia object "callable" by adding methods to its type. (Such "callable" objects are sometimes called "functors.") An example is this accumulator mutable struct (based on Paul Graham's study on programming language syntax and clarity): [5]
In the spirit of imperative programming, an abstract data structure is conceived as an entity that is mutable—meaning that there is a notion of time and the ADT may be in different states at different times. Operations then change the state of the ADT over time; therefore, the order in which operations are evaluated is important, and the same ...
In C++, a const-correct implementation of Cart would allow the user to create instances of the class and then use them as either const (immutable) or mutable, as desired, by providing two different versions of the items() method. (Notice that in C++ it is not necessary — and in fact impossible — to provide a specialized constructor for ...