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6,801 | Here is a C++ header file for the STUDENT class in a simple school application: |
6,802 | Here is a C++ source file for the STUDENT class in a simple school application: |
6,803 | Here is a driver program for demonstration: |
6,804 | Here is a makefile to compile everything: |
6,805 | In functional programming, functions are treated as first-class citizens, meaning that they can be bound to names , passed as arguments, and returned from other functions, just as any other data type can. This allows programs to be written in a declarative and composable style, where small functions are combined in a m... |
6,806 | Functional programming is sometimes treated as synonymous with purely functional programming, a subset of functional programming which treats all functions as deterministic mathematical functions, or pure functions. When a pure function is called with some given arguments, it will always return the same result, and can... |
6,807 | Functional programming has its roots in academia, evolving from the lambda calculus, a formal system of computation based only on functions. Functional programming has historically been less popular than imperative programming, but many functional languages are seeing use today in industry and education, including Comm... |
6,808 | The lambda calculus, developed in the 1930s by Alonzo Church, is a formal system of computation built from function application. In 1937 Alan Turing proved that the lambda calculus and Turing machines are equivalent models of computation, showing that the lambda calculus is Turing complete. Lambda calculus forms the ba... |
6,809 | Church later developed a weaker system, the simply-typed lambda calculus, which extended the lambda calculus by assigning a data type to all terms. This forms the basis for statically typed functional programming. |
6,810 | The first high-level functional programming language, Lisp, was developed in the late 1950s for the IBM 700/7000 series of scientific computers by John McCarthy while at Massachusetts Institute of Technology . Lisp functions were defined using Church's lambda notation, extended with a label construct to allow recursive... |
6,811 | Information Processing Language , 1956, is sometimes cited as the first computer-based functional programming language. It is an assembly-style language for manipulating lists of symbols. It does have a notion of generator, which amounts to a function that accepts a function as an argument, and, since it is an assembly... |
6,812 | Kenneth E. Iverson developed APL in the early 1960s, described in his 1962 book A Programming Language . APL was the primary influence on John Backus's FP. In the early 1990s, Iverson and Roger Hui created J. In the mid-1990s, Arthur Whitney, who had previously worked with Iverson, created K, which is used commercially... |
6,813 | In the mid-1960s, Peter Landin invented SECD machine, the first abstract machine for a functional programming language, described a correspondence between ALGOL 60 and the lambda calculus, and proposed the ISWIM programming language. |
6,814 | John Backus presented FP in his 1977 Turing Award lecture "Can Programming Be Liberated From the von Neumann Style? A Functional Style and its Algebra of Programs". He defines functional programs as being built up in a hierarchical way by means of "combining forms" that allow an "algebra of programs"; in modern languag... |
6,815 | The 1973 language ML was created by Robin Milner at the University of Edinburgh, and David Turner developed the language SASL at the University of St Andrews. Also in Edinburgh in the 1970s, Burstall and Darlington developed the functional language NPL. NPL was based on Kleene Recursion Equations and was first introduc... |
6,816 | In the 1970s, Guy L. Steele and Gerald Jay Sussman developed Scheme, as described in the Lambda Papers and the 1985 textbook Structure and Interpretation of Computer Programs. Scheme was the first dialect of lisp to use lexical scoping and to require tail-call optimization, features that encourage functional programmin... |
6,817 | In the 1980s, Per Martin-Löf developed intuitionistic type theory , which associated functional programs with constructive proofs expressed as dependent types. This led to new approaches to interactive theorem proving and has influenced the development of subsequent functional programming languages. |
6,818 | The lazy functional language, Miranda, developed by David Turner, initially appeared in 1985 and had a strong influence on Haskell. With Miranda being proprietary, Haskell began with a consensus in 1987 to form an open standard for functional programming research; implementation releases have been ongoing as of 1990. |
6,819 | More recently it has found use in niches such as parametric CAD in the OpenSCAD language built on the CGAL framework, although its restriction on reassigning values has led to confusion among users who are unfamiliar with functional programming as a concept. |
6,820 | Functional programming continues to be used in commercial settings. |
6,821 | A number of concepts and paradigms are specific to functional programming, and generally foreign to imperative programming . However, programming languages often cater to several programming paradigms, so programmers using "mostly imperative" languages may have utilized some of these concepts. |
6,822 | Higher-order functions are closely related to first-class functions in that higher-order functions and first-class functions both allow functions as arguments and results of other functions. The distinction between the two is subtle: "higher-order" describes a mathematical concept of functions that operate on other fun... |
6,823 | Higher-order functions enable partial application or currying, a technique that applies a function to its arguments one at a time, with each application returning a new function that accepts the next argument. This lets a programmer succinctly express, for example, the successor function as the addition operator partia... |
6,824 | Pure functions have no side effects . This means that pure functions have several useful properties, many of which can be used to optimize the code: |
6,825 | While most compilers for imperative programming languages detect pure functions and perform common-subexpression elimination for pure function calls, they cannot always do this for pre-compiled libraries, which generally do not expose this information, thus preventing optimizations that involve those external functions... |
6,826 | Iteration in functional languages is usually accomplished via recursion. Recursive functions invoke themselves, letting an operation be repeated until it reaches the base case. In general, recursion requires maintaining a stack, which consumes space in a linear amount to the depth of recursion. This could make recursi... |
6,827 | The Scheme language standard requires implementations to support proper tail recursion, meaning they must allow an unbounded number of active tail calls. Proper tail recursion is not simply an optimization; it is a language feature that assures users that they can use recursion to express a loop and doing so would be s... |
6,828 | Common patterns of recursion can be abstracted away using higher-order functions, with catamorphisms and anamorphisms being the most obvious examples. Such recursion schemes play a role analogous to built-in control structures such as loops in imperative languages. |
6,829 | Most general purpose functional programming languages allow unrestricted recursion and are Turing complete, which makes the halting problem undecidable, can cause unsoundness of equational reasoning, and generally requires the introduction of inconsistency into the logic expressed by the language's type system. Some sp... |
6,830 | Functional languages can be categorized by whether they use strict or non-strict evaluation, concepts that refer to how function arguments are processed when an expression is being evaluated. The technical difference is in the denotational semantics of expressions containing failing or divergent computations. Under s... |
6,831 | fails under strict evaluation because of the division by zero in the third element of the list. Under lazy evaluation, the length function returns the value 4 , since evaluating it does not attempt to evaluate the terms making up the list. In brief, strict evaluation always fully evaluates function arguments before inv... |
6,832 | The usual implementation strategy for lazy evaluation in functional languages is graph reduction. Lazy evaluation is used by default in several pure functional languages, including Miranda, Clean, and Haskell. |
6,833 | Hughes 1984 argues for lazy evaluation as a mechanism for improving program modularity through separation of concerns, by easing independent implementation of producers and consumers of data streams. Launchbury 1993 describes some difficulties that lazy evaluation introduces, particularly in analyzing a program's stor... |
6,834 | Especially since the development of Hindley–Milner type inference in the 1970s, functional programming languages have tended to use typed lambda calculus, rejecting all invalid programs at compilation time and risking false positive errors, as opposed to the untyped lambda calculus, that accepts all valid programs at c... |
6,835 | Some research-oriented functional languages such as Coq, Agda, Cayenne, and Epigram are based on intuitionistic type theory, which lets types depend on terms. Such types are called dependent types. These type systems do not have decidable type inference and are difficult to understand and program with. But dependent ty... |
6,836 | A limited form of dependent types called generalized algebraic data types can be implemented in a way that provides some of the benefits of dependently typed programming while avoiding most of its inconvenience. GADT's are available in the Glasgow Haskell Compiler, in OCaml and in Scala, and have been proposed as addi... |
6,837 | Functional programs do not have assignment statements, that is, the value of a variable in a functional program never changes once defined. This eliminates any chances of side effects because any variable can be replaced with its actual value at any point of execution. So, functional programs are referentially transpar... |
6,838 | Consider C assignment statement x=x * 10, this changes the value assigned to the variable x. Let us say that the initial value of x was 1, then two consecutive evaluations of the variable x yields 10 and 100 respectively. Clearly, replacing x=x * 10 with either 10 or 100 gives a program a different meaning, and so the ... |
6,839 | Now, consider another function such as int plusone {return x+1;} is transparent, as it does not implicitly change the input x and thus has no such side effects.
Functional programs exclusively use this type of function and are therefore referentially transparent. |
6,840 | Purely functional data structures are often represented in a different way to their imperative counterparts. For example, the array with constant access and update times is a basic component of most imperative languages, and many imperative data-structures, such as the hash table and binary heap, are based on arrays. ... |
6,841 | Functional programming is very different from imperative programming. The most significant differences stem from the fact that functional programming avoids side effects, which are used in imperative programming to implement state and I/O. Pure functional programming completely prevents side-effects and provides refere... |
6,842 | Higher-order functions are rarely used in older imperative programming. A traditional imperative program might use a loop to traverse and modify a list. A functional program, on the other hand, would probably use a higher-order "map" function that takes a function and a list, generating and returning a new list by appl... |
6,843 | The following two examples achieve the same effect: they multiply all even numbers in an array by 10 and add them all, storing the final sum in the variable "result". |
6,844 | Traditional Imperative Loop: |
6,845 | Functional Programming with higher-order functions: |
6,846 | There are tasks that often seem most naturally implemented with state. Pure functional programming performs these tasks, and I/O tasks such as accepting user input and printing to the screen, in a different way. |
6,847 | The pure functional programming language Haskell implements them using monads, derived from category theory. Monads offer a way to abstract certain types of computational patterns, including modeling of computations with mutable state in an imperative manner without losing purity. While existing monads may be easy to... |
6,848 | Functional languages also simulate states by passing around immutable states. This can be done by making a function accept the state as one of its parameters, and return a new state together with the result, leaving the old state unchanged. |
6,849 | Impure functional languages usually include a more direct method of managing mutable state. Clojure, for example, uses managed references that can be updated by applying pure functions to the current state. This kind of approach enables mutability while still promoting the use of pure functions as the preferred way to ... |
6,850 | Alternative methods such as Hoare logic and uniqueness have been developed to track side effects in programs. Some modern research languages use effect systems to make the presence of side effects explicit. |
6,851 | Functional programming languages are typically less efficient in their use of CPU and memory than imperative languages such as C and Pascal. This is related to the fact that some mutable data structures like arrays have a very straightforward implementation using present hardware. Flat arrays may be accessed very effi... |
6,852 | Immutability of data can in many cases lead to execution efficiency by allowing the compiler to make assumptions that are unsafe in an imperative language, thus increasing opportunities for inline expansion. |
6,853 | Lazy evaluation may also speed up the program, even asymptotically, whereas it may slow it down at most by a constant factor . Launchbury 1993 discusses theoretical issues related to memory leaks from lazy evaluation, and O'Sullivan et al. 2008 give some practical advice for analyzing and fixing them.
However, the most... |
6,854 | It is possible to use a functional style of programming in languages that are not traditionally considered functional languages. For example, both D and Fortran 95 explicitly support pure functions. |
6,855 | JavaScript, Lua, Python and Go had first class functions from their inception. Python had support for "lambda", "map", "reduce", and "filter" in 1994, as well as closures in Python 2.2, though Python 3 relegated "reduce" to the functools standard library module. First-class functions have been introduced into other ma... |
6,856 | In PHP, anonymous classes, closures and lambdas are fully supported. Libraries and language extensions for immutable data structures are being developed to aid programming in the functional style. |
6,857 | In Java, anonymous classes can sometimes be used to simulate closures; however, anonymous classes are not always proper replacements to closures because they have more limited capabilities. Java 8 supports lambda expressions as a replacement for some anonymous classes. |
6,858 | In C#, anonymous classes are not necessary, because closures and lambdas are fully supported. Libraries and language extensions for immutable data structures are being developed to aid programming in the functional style in C#. |
6,859 | Many object-oriented design patterns are expressible in functional programming terms: for example, the strategy pattern simply dictates use of a higher-order function, and the visitor pattern roughly corresponds to a catamorphism, or fold. |
6,860 | Similarly, the idea of immutable data from functional programming is often included in imperative programming languages, for example the tuple in Python, which is an immutable array, and Object.freeze in JavaScript. |
6,861 | Logic programming can be viewed as a generalisation of functional programming, in which functions are a special case of relations.
For example, the function, mother = Y, can be represented by the relation mother. Whereas functions have a strict input-output pattern of arguments, relations can be queried with any patte... |
6,862 | The program can be queried, like a functional program, to generate mothers from children: |
6,863 | But it can also be queried backwards, to generate children: |
6,864 | It can even be used to generate all instances of the mother relation: |
6,865 | Compared with relational syntax, functional syntax is a more compact notation for nested functions. For example, the definition of maternal grandmother in functional syntax can be written in the nested form: |
6,866 | The same definition in relational notation needs to be written in the unnested form: |
6,867 | Here :- means if and , means and. |
6,868 | However, the difference between the two representations is simply syntactic. In Ciao Prolog, relations can be nested, like functions in functional programming: |
6,869 | Ciao transforms the function-like notation into relational form and executes the resulting logic program using the standard Prolog execution strategy. |
6,870 | Spreadsheets can be considered a form of pure, zeroth-order, strict-evaluation functional programming system. However, spreadsheets generally lack higher-order functions as well as code reuse, and in some implementations, also lack recursion. Several extensions have been developed for spreadsheet programs to enable hig... |
6,871 | Functional programming is an active area of research in the field of programming language theory. There are several peer-reviewed publication venues focusing on functional programming, including the International Conference on Functional Programming, the Journal of Functional Programming, and the Symposium on Trends in... |
6,872 | Functional programming has been employed in a wide range of industrial applications. For example, Erlang, which was developed by the Swedish company Ericsson in the late 1980s, was originally used to implement fault-tolerant telecommunications systems, but has since become popular for building a range of applications a... |
6,873 | Other functional programming languages that have seen use in industry include Scala, F#, Wolfram Language, Lisp, Standard ML and Clojure. |
6,874 | Functional "platforms" have been popular in finance for risk analytics . Risk factors are coded as functions that form interdependent graphs to measure correlations in market shifts, similar in manner to Gröbner basis optimizations but also for regulatory frameworks such as Comprehensive Capital Analysis and Review. G... |
6,875 | Many universities teach functional programming. Some treat it as an introductory programming concept while others first teach imperative programming methods. |
6,876 | Outside of computer science, functional programming is used to teach problem-solving, algebraic and geometric concepts. It has also been used to teach classical mechanics, as in the book Structure and Interpretation of Classical Mechanics. |
6,877 | Abelson, Hal; Sussman, Gerald Jay . Structure and Interpretation of Computer Programs. MIT Press. |
6,878 | Cousineau, Guy and Michel Mauny. The Functional Approach to Programming. Cambridge, UK: Cambridge University Press, 1998. |
6,879 | Curry, Haskell Brooks and Feys, Robert and Craig, William. Combinatory Logic. Volume I. North-Holland Publishing Company, Amsterdam, 1958. |
6,880 | Curry, Haskell B.; Hindley, J. Roger; Seldin, Jonathan P. . Combinatory Logic. Vol. II. Amsterdam: North Holland. ISBN 978-0-7204-2208-5. |
6,881 | Dominus, Mark Jason. Higher-Order Perl. Morgan Kaufmann. 2005. |
6,882 | Felleisen, Matthias; Findler, Robert; Flatt, Matthew; Krishnamurthi, Shriram . How to Design Programs. MIT Press. |
6,883 | Graham, Paul. ANSI Common LISP. Englewood Cliffs, New Jersey: Prentice Hall, 1996. |
6,884 | MacLennan, Bruce J. Functional Programming: Practice and Theory. Addison-Wesley, 1990. |
6,885 | Michaelson, Greg . An Introduction to Functional Programming Through Lambda Calculus. Courier Corporation. ISBN 978-0-486-28029-5. |
6,886 | O'Sullivan, Brian; Stewart, Don; Goerzen, John . Real World Haskell. O'Reilly. |
6,887 | Pratt, Terrence W. and Marvin Victor Zelkowitz. Programming Languages: Design and Implementation. 3rd ed. Englewood Cliffs, New Jersey: Prentice Hall, 1996. |
6,888 | Salus, Peter H. Functional and Logic Programming Languages. Vol. 4 of Handbook of Programming Languages. Indianapolis, Indiana: Macmillan Technical Publishing, 1998. |
6,889 | Thompson, Simon. Haskell: The Craft of Functional Programming. Harlow, England: Addison-Wesley Longman Limited, 1996. |
6,890 | Paradigms are separated along and described by different dimensions of programming. Some paradigms are about implications of the execution model, such as allowing side effects, or whether the sequence of operations is defined by the execution model. Other paradigms are about the way code is organized, such as grouping ... |
6,891 | Some common programming paradigms include : |
6,892 | Programming paradigms come from computer science research into existing practices of software development. The findings allow for describing and comparing programming practices and the languages used to code programs. For perspective, other research studies
software engineering processes and describes various methodol... |
6,893 | A programming language can be described in terms of paradigms. Some languages support only one paradigm. For example, Smalltalk supports object-oriented and Haskell supports functional. Most languages support multiple paradigms. For example, a program written in C++, Object Pascal or PHP can be purely procedural, purel... |
6,894 | When using a language that supports multiple paradigms, the developer chooses which paradigm elements to use. But, this choice may not involve considering paradigms per se. The developer often uses the features of a language as the language provides them and to the extent that the developer knows them. Categorizing the... |
6,895 | Languages categorized as imperative paradigm have two main features: they state the order in which operations occur, with constructs that explicitly control that order, and they allow side effects, in which state can be modified at one point in time, within one unit of code, and then later read at a different point in ... |
6,896 | In contrast, languages in the declarative paradigm do not state the order in which to execute operations. Instead, they supply a number of available operations in the system, along with the conditions under which each is allowed to execute. The implementation of the language's execution model tracks which operations a... |
6,897 | In object-oriented programming, code is organized into objects that contain state that is owned by and controlled by the code of the object. Most object-oriented languages are also imperative languages. |
6,898 | In object-oriented programming, programs are treated as a set of interacting objects. In functional programming, programs are treated as a sequence of stateless function evaluations. When programming computers or systems with many processors, in process-oriented programming, programs are treated as sets of concurrent p... |
6,899 | Many programming paradigms are as well known for the techniques they forbid as for those they support. For instance, pure functional programming disallows side-effects, while structured programming disallows the goto construct. Partly for this reason, new paradigms are often regarded as doctrinaire or overly rigid by t... |
6,900 | Programming paradigms can also be compared with programming models, which allows invoking an execution model by using only an API. Programming models can also be classified into paradigms based on features of the execution model. |
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