We present our experience with teaching functional programming and F# to experienced.NET developers through a book Real-World Functional Program- ming and commercially offered F# trainings. The most important novelty in our approach is the use of C# for relating functional F# with object-oriented C# and.

• • • In, functional programming is a —a style of building the structure and elements of —that treats as the evaluation of and avoids changing- and data. It is a paradigm, which means programming is done with or declarations instead of. In functional code, the output value of a function depends only on the that are passed to the function, so calling a function f twice with the same value for an argument x produces the same result f(x) each time; this is in contrast to depending on a or, which may produce different results at different times when called with the same arguments but a different program state. Eliminating, i.e., changes in state that do not depend on the function inputs, can make it much easier to understand and predict the behavior of a program, which is one of the key motivations for the development of functional programming. Functional programming has its origins in, a developed in the 1930s to investigate, the, function definition,, and. Many functional can be viewed as elaborations on the lambda calculus.

Another well-known declarative programming paradigm,, is based on. In contrast, changes state with commands in the, the simplest example being. Imperative programming does have functions—not in the mathematical sense—but in the sense of. They can have that may change the value of program state. Functions without therefore make sense. Because of this, they lack, i.e., the same language expression can result in different values at different times depending on the state of the executing program. Functional programming languages have largely been emphasized in rather than in commercial software development.

However, prominent programming languages that support functional programming such as,,, (also known as ),,,,, and have been used in industrial and commercial applications by a wide variety of organizations., one of the world's most widely distributed languages, has the properties of an untyped functional language, in addition to imperative and object-oriented paradigms. Functional programming is also supported in some like (statistics),, and (financial analysis), / (), and. Widespread domain-specific declarative languages like and / use some elements of functional programming, especially in eschewing. Programming in a functional style can also be accomplished in languages that are not specifically designed for functional programming. For example, the imperative programming language has been the subject of a book describing how to apply functional programming concepts.

This is also true of the programming language.,, and all added constructs to facilitate the functional style. The language also offers functional programming abilities. An interesting case is that of – it is frequently written in a functional style, but the presence of side effects and mutable state place it in a grey area between imperative and functional languages. Contents • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • History [ ] provides a theoretical framework for describing functions and their evaluation. It is a mathematical abstraction rather than a programming language—but it forms the basis of almost all current functional programming languages. An equivalent theoretical formulation,, is commonly perceived as more abstract than lambda calculus and preceded it in invention. Combinatory logic and lambda calculus were both originally developed to achieve a clearer approach to the.

An early functional-flavored language was, developed in the late 1950s for the scientific computers by while at (MIT). Lisp first introduced many paradigmatic features of functional programming, though early Lisps were, and incorporated support for numerous programming styles as new paradigms evolved.

Later dialects, such as and, and offshoots such as and, sought to simplify and rationalise Lisp around a cleanly functional core, while was designed to preserve and update the paradigmatic features of the numerous older dialects it replaced. (IPL) is sometimes cited as the first computer-based functional programming language. It is an 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-level language, code can be data, so IPL can be regarded as having higher-order functions. However, it relies heavily on mutating list structure and similar imperative features. Developed in the early 1960s, described in his 1962 book A Programming Language ( ).

APL was the primary influence on 's. In the early 1990s, Iverson and created. In the mid-1990s,, who had previously worked with Iverson, created, which is used commercially in financial industries along with its descendant. Presented in his 1977 lecture 'Can Programming Be Liberated From the 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 language, this means that functional programs follow the [ ]. Backus's paper popularized research into functional programming, though it emphasized rather than the lambda-calculus style now associated with functional programming. In the 1970s, was created by at the, and initially developed the language at the and later the language at the. Also in Edinburgh in the 1970s, Burstall and Darlington developed the functional language. NPL was based on and was first introduced in their work on program transformation.

Burstall, MacQueen and Sannella then incorporated the polymorphic type checking from ML to produce the language. ML eventually developed into several dialects, the most common of which are now and. Meanwhile, the development of, a simple and (impurely) functional dialect of Lisp, as described in the influential and the classic 1985 textbook, brought awareness of the power of functional programming to the wider programming-languages community. In the 1980s, developed (also called constructive type theory), which associated functional programs with of arbitrarily complex mathematical propositions expressed as. This led to powerful new approaches to and has influenced the development of many subsequent functional programming languages. The began with a consensus in 1987 to form an for functional programming research; implementation releases have been ongoing since 1990. Concepts [ ] A number of concepts and paradigms are specific to functional programming, and generally foreign to (including ).

However, programming languages are often hybrids of several programming paradigms, so programmers using 'mostly imperative' languages may have utilized some of these concepts. First-class and higher-order functions [ ].

Main article: (looping) in functional languages is usually accomplished via. Invoke themselves, letting an operation be repeated until it reaches the. Though some recursion requires maintaining a stack, can be recognized and optimized by a compiler into the same code used to implement iteration in imperative languages. The language standard requires implementations to recognize and optimize tail recursion.

Tail recursion optimization can be implemented by transforming the program into during compiling, among other approaches. Common patterns of recursion can be factored out using higher order functions, with and (or 'folds' and 'unfolds') being the most obvious examples. Such higher order functions play a role analogous to built-in control structures such as in. Most general purpose functional programming languages allow unrestricted recursion and are, which makes the, can cause unsoundness of, and generally requires the introduction of into the logic expressed by the language's. Some special purpose languages such as allow only recursion and are (nonterminating computations can be expressed only with infinite streams of values called ).

As a consequence, these languages fail to be Turing complete and expressing certain functions in them is impossible, but they can still express a wide class of interesting computations while avoiding the problems introduced by unrestricted recursion. Functional programming limited to well-founded recursion with a few other constraints is called. Strict versus non-strict evaluation [ ]. Main article: Functional languages can be categorized by whether they use strict (eager) or non-strict (lazy) evaluation, concepts that refer to how function arguments are processed when an expression is being evaluated. The technical difference is in the of expressions containing failing or divergent computations. Under strict evaluation, the evaluation of any term containing a failing subterm fails.

For example, the expression: print length([2+1, 3*2, 1/0, 5-4]) 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 (i.e., the number of items in the list), since evaluating it does not attempt to evaluate the terms making up the list. In brief, strict evaluation always fully evaluates function arguments before invoking the function. Lazy evaluation does not evaluate function arguments unless their values are required to evaluate the function call itself. The usual implementation strategy for lazy evaluation in functional languages is.

Call Of Duty 4 Profile Download Level 55 100. Lazy evaluation is used by default in several pure functional languages, including,, and. Argues for lazy evaluation as a mechanism for improving program modularity through, 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 storage requirements, and proposes an to aid in such analysis. Harper 2009 proposes including both strict and lazy evaluation in the same language, using the language's type system to distinguish them.

Type systems [ ] Especially since the development of in the 1970s, functional programming languages have tended to use, rejecting all invalid programs at compilation time and risking, as opposed to the, that accepts all valid programs at compilation time and risks, used in Lisp and its variants (such as ), though they reject all invalid programs at runtime, when the information is enough to not reject valid programs. The use of makes manipulation of complex data structures convenient; the presence of strong compile-time type checking makes programs more reliable in absence of other reliability techniques like, while frees the programmer from the need to manually declare types to the compiler in most cases. Some research-oriented functional languages such as,,, and are based on, which lets types depend on terms. Such types are called. These type systems do not have decidable type inference and are difficult to understand and program with [ ].

But dependent types can express arbitrary propositions in. Through the, then, well-typed programs in these languages become a means of writing formal from which a compiler can generate. While these languages are mainly of interest in academic research (including in ), they have begun to be used in engineering as well. Is a for a subset of the that is written in Coq and formally verified.

A limited form of dependent types called (GADT's) 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, in (since version 4.00) and in (as 'case classes'), and have been proposed as additions to other languages including Java and C#. Referential transparency [ ]. Main article: Purely functional are often represented in a different way than their counterparts. For example, the with constant access and update times is a basic component of most imperative languages, and many imperative data-structures, such as the and, are based on arrays. Arrays can be replaced by or, which admit purely functional implementation, but have access and update times.

Therefore, purely functional data structures can be used in non-functional languages, but they may not be the most efficient tool, especially if persistence is not required. Comparison to imperative programming [ ] Functional programming is very different from. The most significant differences stem from the fact that functional programming avoids, which are used in imperative programming to implement state and I/O. Pure functional programming completely prevents side-effects and provides.

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 applying the function to each list item. Simulating state [ ] There are tasks (for example, maintaining a bank account balance) 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.

The pure functional programming language implements them using, derived from. Monads offer a way to abstract certain types of computational patterns, including (but not limited to) modeling of computations with mutable state (and other side effects such as I/O) in an imperative manner without losing purity. While existing monads may be easy to apply in a program, given appropriate templates and examples, many students find them difficult to understand conceptually, e.g., when asked to define new monads (which is sometimes needed for certain types of libraries). Another way that functional languages can simulate state is by passing around a that represents the current state as a parameter to function calls.

On each function call, a copy of this data structure is created with whatever differences are the result of the function. This is referred to as '. Impure functional languages usually include a more direct method of managing mutable state., 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 express computations. Alternative methods such as and have been developed to track side effects in programs. Some modern research languages use to make the presence of side effects explicit.

Efficiency issues [ ] Functional programming languages are typically less efficient in their use of and memory than imperative languages such as and. This is related to the fact that some mutable data structures like arrays have a very straightforward implementation using present hardware (which is a highly evolved Turing machine). Flat arrays may be accessed very efficiently with deeply pipelined CPUs, prefetched efficiently through caches (with no complex ), or handled with SIMD instructions. It is also not easy to create their equally efficient general-purpose immutable counterparts.

For purely functional languages, the worst-case slowdown is logarithmic in the number of memory cells used, because mutable memory can be represented by a purely functional data structure with logarithmic access time (such as a balanced tree). However, such slowdowns are not universal. For programs that perform intensive numerical computations, functional languages such as and are only slightly slower than C according to. For programs that handle large and multidimensional, functional languages (such as and ) were designed with speed optimizations. 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.

May also speed up the program, even asymptotically, whereas it may slow it down at most by a constant factor (however, it may introduce if used improperly). 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 general implementations of lazy evaluation making extensive use of dereferenced code and data perform poorly on modern processors with deep pipelines and multi-level caches (where a cache miss may cost hundreds of cycles) [ ]. Coding styles [ ].

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8.0,,,,,: compiler: dual and MIT/X11 Libraries: 2: dual and 2.cs Website Major,,,,,, Influenced by,,,,,,,,,,,,, Influenced,,,,,,,,,,,,,,, • at Wikibooks C# (pronounced as see sharp) is a encompassing,,,,, (-based), and programming disciplines. It was developed by within its initiative and later approved as a standard by (ECMA-334) and (ISO/IEC ). C# is one of the programming languages designed for the.

C# is a general-purpose, object-oriented programming language. Its development team is led. The most recent version is C# 7.2, which was released in 2017 along with Visual Studio 2017 version 15.5. Contents • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Design goals [ ] The ECMA standard lists these design goals for C#: • The language is intended to be a simple, modern, general-purpose, language. • The language, and implementations thereof, should provide support for software engineering principles such as checking, array, detection of attempts to use, and automatic.

Software robustness, durability, and programmer productivity are important. • The language is intended for use in developing suitable for deployment in distributed environments. • Portability is very important for source code and programmers, especially those already familiar with and. • Support for is very important.

• C# is intended to be suitable for writing applications for both hosted and, ranging from the very large that use sophisticated, down to the very small having dedicated functions. • Although C# applications are intended to be economical with regard to memory and requirements, the language was not intended to compete directly on performance and size with C or assembly language.

History [ ] During the development of the.NET Framework, the were originally written using a compiler system called Simple Managed C (SMC). In January 1999, formed a team to build a new language at the time called Cool, which stood for ' Object Oriented Language'.

Microsoft had considered keeping the name 'Cool' as the final name of the language, but chose not to do so for trademark reasons. By the time the.NET project was publicly announced at the July 2000, the language had been renamed C#, and the class libraries and runtime had been ported to C#. Hejlsberg is C#'s principal designer and lead architect at Microsoft, and was previously involved with the design of, (formerly CodeGear Delphi, Inprise Delphi and Borland Delphi), and. In interviews and technical papers he has stated that flaws [ ] in most major programming languages (e.g.,,, and ) drove the fundamentals of the (CLR), which, in turn, drove the design of the C# language itself., who created the programming language in 1994, and, a co-founder of Sun Microsystems, the originator of Java, called C# an 'imitation' of Java; Gosling further said that '[C# is] sort of Java with reliability, productivity and security deleted.' Klaus Kreft and Angelika Langer (authors of a C++ streams book) stated in a blog post that 'Java and C# are almost identical programming languages.

Boring repetition that lacks innovation,' 'Hardly anybody will claim that Java or C# are revolutionary programming languages that changed the way we write programs,' and 'C# borrowed a lot from Java - and vice versa. Now that C# supports and unboxing, we'll have a very similar feature in Java.' In July 2000, Hejlsberg said that C# is 'not a Java clone' and is 'much closer to C++' in its design.

Since the release of C# 2.0 in November 2005, the C# and Java languages have evolved on increasingly divergent trajectories, becoming somewhat less similar. One of the first major departures came with the addition of to both languages, with vastly different implementations. C# makes use of to provide 'first-class' generic objects that can be used like any other class, with code generation performed at class-load time. Furthermore, C# has added several major features to accommodate functional-style programming, culminating in the extensions released with C# 3.0 and its supporting framework of,, and. These features enable C# programmers to use functional programming techniques, such as, when it is advantageous to their application.

The LINQ extensions and the functional imports help developers reduce the amount of that is included in common tasks like querying a database, parsing an xml file, or searching through a data structure, shifting the emphasis onto the actual program logic to help improve readability and maintainability. C# used to have a called Andy (named after Anders Hejlsberg). It was retired on January 29, 2004. C# was originally submitted to the ISO subcommittee JTC 1/SC 22 for review, under ISO/IEC, was withdrawn and was then approved under ISO/IEC. The name 'C sharp' was inspired by musical notation where a indicates that the written note should be made a higher in. This is similar to the language name of, where '++' indicates that a variable should be incremented by 1.

The sharp symbol also resembles a of four '+' symbols (in a two-by-two grid), further implying that the language is an increment of C++. Due to technical limitations of display (standard fonts, browsers, etc.) and the fact that the sharp symbol ( U+266F ♯ (HTML ♯)) is not present on most, the ( U+0023 # NUMBER SIGN (HTML #)) was chosen to approximate the sharp symbol in the written name of the programming language. This convention is reflected in the ECMA-334 C# Language Specification. However, when it is practical to do so (for example, in advertising or in box art ), Microsoft uses the intended musical symbol.

The 'sharp' suffix has been used by a number of other.NET languages that are variants of existing languages, including (a.NET language also designed by Microsoft that is derived from Java 1.1), (from ), and the language. The original implementation of was called Eiffel#, a name retired since the full language is now supported.

The suffix has also been used for, such as (a.NET for and other libraries) and (a wrapper for ). See also: Some notable features of C# that distinguish it from C, C++, and Java where noted, are: Portability [ ] By design, C# is the programming language that most directly reflects the underlying (CLI). Most of its intrinsic types correspond to value-types implemented by the CLI framework. However, the language specification does not state the code generation requirements of the compiler: that is, it does not state that a C# compiler must target a Common Language Runtime, or generate (CIL), or generate any other specific format. Theoretically, a C# compiler could generate machine code like traditional compilers of C++. Typing [ ] C# supports strongly typed implicit variable declarations with the keyword var, and implicitly typed arrays with the keyword new[] followed by a collection initializer. C# supports a strict, bool.

Statements that take conditions, such as while and if, require an expression of a type that implements the true operator, such as the Boolean type. While C++ also has a Boolean type, it can be freely converted to and from integers, and expressions such as if(a) require only that a is convertible to bool, allowing a to be an int, or a pointer.

C# disallows this 'integer meaning true or false' approach, on the grounds that forcing programmers to use expressions that return exactly bool can prevent certain types of programming mistakes such as if (a = b) (use of assignment = instead of equality ==, which while not an error in C or C++, will be caught by the compiler anyway). C# is more than C++. The only implicit conversions by default are those that are considered safe, such as widening of integers. This is enforced at compile-time, during, and, in some cases, at runtime. No implicit conversions occur between Booleans and integers, nor between enumeration members and integers (except for literal 0, which can be implicitly converted to any enumerated type).

Any user-defined conversion must be explicitly marked as explicit or implicit, unlike C++ and conversion operators, which are both implicit by default. C# has explicit support for in generic types, unlike C++ which has some degree of support for contravariance simply through the semantics of return types on virtual methods. Members are placed in their own. The C# language does not allow for global variables or functions. All methods and members must be declared within classes. Static members of public classes can substitute for global variables and functions.

Local variables cannot variables of the enclosing block, unlike C and C++. Metaprogramming [ ] via C# attributes is part of the language. Many of these attributes duplicate the functionality of GCC's and VisualC++'s platform-dependent preprocessor directives. Methods and functions [ ] Methods in programming language are the members of a class in a project, some methods have signatures and some don't have signatures. Methods can be void or can return something like string, integer, double, decimal, float and bool.

If a method is void it means that the method does not return any data type. Like C++, and unlike Java, C# programmers must use the keyword virtual to allow methods to be overridden by subclasses. Extension methods in C# allow programmers to use static methods as if they were methods from a class's method table, allowing programmers to add methods to an object that they feel should exist on that object and its derivatives. The type dynamic allows for run-time method binding, allowing for JavaScript-like method calls and run-time object composition. C# has support for strongly-typed function pointers via the keyword delegate. Like the Qt framework's pseudo-C++ signal and slot, C# has semantics specifically surrounding publish-subscribe style events, though C# uses delegates to do so.

C# offers Java-like synchronized method calls, via the attribute [MethodImpl(MethodImplOptions.Synchronized)], and has support for via the keyword lock. Property [ ] C# provides as for a common pattern in which a pair of methods, encapsulate operations on a single of a class.

No redundant method signatures for the getter/setter implementations need be written, and the property may be accessed using attribute syntax rather than more verbose method calls. Namespace [ ] A C# namespace provides the same level of code isolation as a Java package or a C++ namespace, with very similar rules and features to a package. Memory access [ ] In C#, memory address pointers can only be used within blocks specifically marked as unsafe, and programs with unsafe code need appropriate permissions to run. Most object access is done through safe object references, which always either point to a 'live' object or have the well-defined value; it is impossible to obtain a reference to a 'dead' object (one that has been garbage collected), or to a random block of memory. An unsafe pointer can point to an instance of a value-type, array, string, or a block of memory allocated on a stack.

Code that is not marked as unsafe can still store and manipulate pointers through the System.IntPtr type, but it cannot dereference them. Managed memory cannot be explicitly freed; instead, it is automatically garbage collected. Garbage collection addresses the problem of by freeing the programmer of responsibility for releasing memory that is no longer needed. Exception [ ] are not present in C# (in contrast to Java).

This has been a conscious decision based on the issues of scalability and versionability. Polymorphism [ ] Unlike, C# does not support, although a class can implement any number of interfaces. This was a design decision by the language's lead architect to avoid complication and simplify architectural requirements throughout CLI. When implementing multiple interfaces that contain a method with the same signature, C# allows implementing each method depending on which interface that method is being called through, or, like Java, allows implementing the method once, and have that be the one invocation on a call through any of the class's interfaces.

However, unlike, C# supports. Only the most commonly overloaded operators in C++ may be overloaded in C#. Language Integrated Query - LINQ [ ] C# has the ability to utilize LINQ through the Microsoft.NET Framework with the IEnumerable Interface a developer can query any.NET collection class, XML documents, ADO.NET datasets, and SQL databases. There are some advantages to using LINQ in C# and they are as follows: intellisense support, strong filtering capabilities, type safety with compile error checking ability, and brings consistency for querying data over a variety of sources. There are several different language structures that can be utilized with C# with LINQ and they are query expressions, lambda expressions, anonymous types, implicitly typed variables, extension methods, and object initializers.

Functional programming [ ] Though primarily an imperative language, C# 2.0 offered limited support for functional programming through and closures in the form of anonymous delegates. C# 3.0 expanded support for functional programming with the introduction of a lightweight syntax for lambda expressions, extension methods (an affordance for modules), and a syntax in the form of a 'query comprehension' language. Common type system [ ] C# has a unified type system. This unified type system is called (CTS).

A unified type system implies that all types, including primitives such as integers, are subclasses of the System. Object class. For example, every type inherits a ToString () method. Categories of data types [ ] CTS separates data types into two categories: • Reference types • Value types Instances of value types do not have referential identity nor referential comparison semantics - equality and inequality comparisons for value types compare the actual data values within the instances, unless the corresponding operators are overloaded.

Value types are derived from System. ValueType, always have a default value, and can always be created and copied. Some other limitations on value types are that they cannot derive from each other (but can implement interfaces) and cannot have an explicit default (parameterless) constructor. Examples of value types are all primitive types, such as int (a signed 32-bit integer), float (a 32-bit IEEE floating-point number), char (a 16-bit Unicode code unit), and System. DateTime (identifies a specific point in time with nanosecond precision). Other examples are enum (enumerations) and struct (user defined structures).

In contrast, reference types have the notion of referential identity - each instance of a reference type is inherently distinct from every other instance, even if the data within both instances is the same. This is reflected in default equality and inequality comparisons for reference types, which test for referential rather than structural equality, unless the corresponding operators are overloaded (such as the case for System.

In general, it is not always possible to create an instance of a reference type, nor to copy an existing instance, or perform a value comparison on two existing instances, though specific reference types can provide such services by exposing a public constructor or implementing a corresponding interface (such as ICloneable or IComparable). Examples of reference types are object (the ultimate base class for all other C# classes), System. String (a string of Unicode characters), and System. Array (a base class for all C# arrays).

Both type categories are extensible with user-defined types. Boxing and unboxing [ ] Boxing is the operation of converting a value-type object into a value of a corresponding reference type. Boxing in C# is implicit. Unboxing is the operation of converting a value of a reference type (previously boxed) into a value of a value type.

Unboxing in C# requires an explicit. A boxed object of type T can only be unboxed to a T (or a nullable T). Using System; The above line of code tells the compiler to use System as a candidate prefix for types used in the source code. In this case, when the compiler sees use of the Console type later in the source code, it tries to find a type named Console, first in the current assembly, followed by all referenced assemblies. In this case the compiler fails to find such a type, since the name of the type is actually System.Console. The compiler then attempts to find a type named System.Console by using the System prefix from the using statement, and this time it succeeds.

The using statement allows the programmer to state all candidate prefixes to use during compilation instead of always using full type names. Static void Main ( string [] args ) This declares the class member method where the program begins execution. The.NET runtime calls the Main method. (Note: Main may also be called from elsewhere, like any other method, e.g. From another method of Program.) The makes the method accessible without an instance of Program. Each console application's Main entry point must be declared static. Otherwise, the program would require an instance, but any instance would require a program.

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