This sample will guide you through elements of the F# language. This sample will guide you through elements of the F# language. To execute the code in F# Interactive, highlight a section of code and press Alt-Enter or right-click To execute the code in F# Interactive, highlight a section of code and press Alt-Enter or right-click and select "Execute in Interactive". You can open the F# Interactive Window from the "View" menu. and select "Execute in Interactive". You can open the F# Interactive Window from the "View" menu. For more about F#, see: For more about F#, see: To see this tutorial in documentation form, see: To see this tutorial in documentation form, see: To learn more about applied F# programming, use To learn more about applied F# programming, use To install the Visual F# Power Tools, use To install the Visual F# Power Tools, use 'Tools' --> 'Extensions and Updates' --> `Online` and search 'Tools' --> 'Extensions and Updates' --> `Online` and search For additional templates to use with F#, see the 'Online Templates' in Visual Studio, For additional templates to use with F#, see the 'Online Templates' in Visual Studio, 'New Project' --> 'Online Templates' 'New Project' --> 'Online Templates' F# supports three kinds of comments: F# supports three kinds of comments: 1. Double-slash comments. These are used in most situations. 1. Double-slash comments. These are used in most situations. 2. ML-style Block comments. These aren't used that often. 2. ML-style Block comments. These aren't used that often. 3. Triple-slash comments. These are used for documenting functions, types, and so on. 3. Triple-slash comments. These are used for documenting functions, types, and so on. They will appear as text when you hover over something which is decorated with these comments. They will appear as text when you hover over something which is decorated with these comments. They also support .NET-style XML comments, which allow you to generate reference documentation, They also support .NET-style XML comments, which allow you to generate reference documentation, and they also allow editors (such as Visual Studio) to extract information from them. and they also allow editors (such as Visual Studio) to extract information from them. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/xml-documentation To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/xml-documentation Open namespaces using the 'open' keyword. Open namespaces using the 'open' keyword. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/import-declarations-the-open-keyword To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/import-declarations-the-open-keyword A module is a grouping of F# code, such as values, types, and function values. A module is a grouping of F# code, such as values, types, and function values. Grouping code in modules helps keep related code together and helps avoid name conflicts in your program. Grouping code in modules helps keep related code together and helps avoid name conflicts in your program. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/modules To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/modules This is a sample integer. This is a sample integer. This is a sample floating point number. This is a sample floating point number. This computed a new number by some arithmetic. Numeric types are converted using This computed a new number by some arithmetic. Numeric types are converted using functions 'int', 'double' and so on. functions 'int', 'double' and so on. This is a list of the numbers from 0 to 99. This is a list of the numbers from 0 to 99. This is a list of all tuples containing all the numbers from 0 to 99 and their squares. This is a list of all tuples containing all the numbers from 0 to 99 and their squares. The next line prints a list that includes tuples, using '%A' for generic printing. The next line prints a list that includes tuples, using '%A' for generic printing. This is a sample integer with a type annotation This is a sample integer with a type annotation Values in F# are immutable by default. They cannot be changed Values in F# are immutable by default. They cannot be changed in the course of a program's execution unless explicitly marked as mutable. in the course of a program's execution unless explicitly marked as mutable. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/values/index#why-immutable To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/values/index#why-immutable Binding a value to a name via 'let' makes it immutable. Binding a value to a name via 'let' makes it immutable. The second line of code fails to compile because 'number' is immutable and bound. The second line of code fails to compile because 'number' is immutable and bound. Re-defining 'number' to be a different value is not allowed in F#. Re-defining 'number' to be a different value is not allowed in F#. A mutable binding. This is required to be able to mutate the value of 'otherNumber'. A mutable binding. This is required to be able to mutate the value of 'otherNumber'. When mutating a value, use '<-' to assign a new value. When mutating a value, use '<-' to assign a new value. You could not use '=' here for this purpose since it is used for equality You could not use '=' here for this purpose since it is used for equality or other contexts such as 'let' or 'module' or other contexts such as 'let' or 'module' Much of F# programming consists of defining functions that transform input data to produce Much of F# programming consists of defining functions that transform input data to produce useful results. useful results. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/functions/ To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/functions/ You use 'let' to define a function. This one accepts an integer argument and returns an integer. You use 'let' to define a function. This one accepts an integer argument and returns an integer. Parentheses are optional for function arguments, except for when you use an explicit type annotation. Parentheses are optional for function arguments, except for when you use an explicit type annotation. Apply the function, naming the function return result using 'let'. Apply the function, naming the function return result using 'let'. The variable type is inferred from the function return type. The variable type is inferred from the function return type. This line uses '%d' to print the result as an integer. This is type-safe. This line uses '%d' to print the result as an integer. This is type-safe. If 'result1' were not of type 'int', then the line would fail to compile. If 'result1' were not of type 'int', then the line would fail to compile. When needed, annotate the type of a parameter name using '(argument:type)'. Parentheses are required. When needed, annotate the type of a parameter name using '(argument:type)'. Parentheses are required. Conditionals use if/then/elid/elif/else. Conditionals use if/then/elid/elif/else. Note that F# uses whitespace indentation-aware syntax, similar to languages like Python. Note that F# uses whitespace indentation-aware syntax, similar to languages like Python. This line uses '%f' to print the result as a float. As with '%d' above, this is type-safe. This line uses '%f' to print the result as a float. As with '%d' above, this is type-safe. Booleans are fundamental data types in F#. Here are some examples of Booleans and conditional logic. Booleans are fundamental data types in F#. Here are some examples of Booleans and conditional logic. To learn more, see: To learn more, see: and and Booleans values are 'true' and 'false'. Booleans values are 'true' and 'false'. Operators on booleans are 'not', '&&' and '||'. Operators on booleans are 'not', '&&' and '||'. This line uses '%b'to print a boolean value. This is type-safe. This line uses '%b'to print a boolean value. This is type-safe. Strings are fundamental data types in F#. Here are some examples of Strings and basic String manipulation. Strings are fundamental data types in F#. Here are some examples of Strings and basic String manipulation. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/strings To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/strings Strings use double quotes. Strings use double quotes. Strings can also use @ to create a verbatim string literal. Strings can also use @ to create a verbatim string literal. This will ignore escape characters such as '\', '\n', '\t', etc. This will ignore escape characters such as '\', '\n', '\t', etc. String literals can also use triple-quotes. String literals can also use triple-quotes. String concatenation is normally done with the '+' operator. String concatenation is normally done with the '+' operator. This line uses '%s' to print a string value. This is type-safe. This line uses '%s' to print a string value. This is type-safe. Substrings use the indexer notation. This line extracts the first 7 characters as a substring. Substrings use the indexer notation. This line extracts the first 7 characters as a substring. Note that like many languages, Strings are zero-indexed in F#. Note that like many languages, Strings are zero-indexed in F#. Tuples are simple combinations of data values into a combined value. Tuples are simple combinations of data values into a combined value. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/tuples To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/tuples A simple tuple of integers. A simple tuple of integers. A function that swaps the order of two values in a tuple. A function that swaps the order of two values in a tuple. F# Type Inference will automatically generalize the function to have a generic type, F# Type Inference will automatically generalize the function to have a generic type, meaning that it will work with any type. meaning that it will work with any type. A tuple consisting of an integer, a string, A tuple consisting of an integer, a string, and a double-precision floating point number. and a double-precision floating point number. A simple tuple of integers with a type annotation. A simple tuple of integers with a type annotation. Type annotations for tuples use the * symbol to separate elements Type annotations for tuples use the * symbol to separate elements Tuples are normally objects, but they can also be represented as structs. Tuples are normally objects, but they can also be represented as structs. These interoperate completely with structs in C# and Visual Basic.NET; however, These interoperate completely with structs in C# and Visual Basic.NET; however, struct tuples are not implicitly convertable with object tuples (often called reference tuples). struct tuples are not implicitly convertable with object tuples (often called reference tuples). The second line below will fail to compile because of this. Uncomment it to see what happens. The second line below will fail to compile because of this. Uncomment it to see what happens. Although you cannot implicitly convert between struct tuples and reference tuples, Although you cannot implicitly convert between struct tuples and reference tuples, you can explicitly convert via pattern matching, as demonstrated below. you can explicitly convert via pattern matching, as demonstrated below. The F# pipe operators ('|>', '<|', etc.) and F# composition operators ('>>', '<<') The F# pipe operators ('|>', '<|', etc.) and F# composition operators ('>>', '<<') are used extensively when processing data. These operators are themselves functions are used extensively when processing data. These operators are themselves functions which make use of Partial Application. which make use of Partial Application. To learn more about these operators, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/functions/#function-composition-and-pipelining To learn more about these operators, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/functions/#function-composition-and-pipelining To learn more about Partial Application, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/functions/#partial-application-of-arguments To learn more about Partial Application, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/functions/#partial-application-of-arguments Squares a value. Squares a value. Adds 1 to a value. Adds 1 to a value. Tests if an integer value is odd via modulo. Tests if an integer value is odd via modulo. A list of 5 numbers. More on lists later. A list of 5 numbers. More on lists later. Given a list of integers, it filters out the even numbers, Given a list of integers, it filters out the even numbers, squares the resulting odds, and adds 1 to the squared odds. squares the resulting odds, and adds 1 to the squared odds. A shorter way to write 'squareOddValuesAndAddOne' is to nest each A shorter way to write 'squareOddValuesAndAddOne' is to nest each sub-result into the function calls themselves. sub-result into the function calls themselves. This makes the function much shorter, but it's difficult to see the This makes the function much shorter, but it's difficult to see the order in which the data is processed. order in which the data is processed. A preferred way to write 'squareOddValuesAndAddOne' is to use F# pipe operators. A preferred way to write 'squareOddValuesAndAddOne' is to use F# pipe operators. This allows you to avoid creating intermediate results, but is much more readable This allows you to avoid creating intermediate results, but is much more readable than nesting function calls like 'squareOddValuesAndAddOneNested' than nesting function calls like 'squareOddValuesAndAddOneNested' You can shorten 'squareOddValuesAndAddOnePipeline' by moving the second `List.map` call You can shorten 'squareOddValuesAndAddOnePipeline' by moving the second `List.map` call into the first, using a Lambda Function. into the first, using a Lambda Function. Note that pipelines are also being used inside the lambda function. F# pipe operators Note that pipelines are also being used inside the lambda function. F# pipe operators can be used for single values as well. This makes them very powerful for processing data. can be used for single values as well. This makes them very powerful for processing data. Lastly, you can eliminate the need to explicitly take 'values' in as a parameter by using '>>' Lastly, you can eliminate the need to explicitly take 'values' in as a parameter by using '>>' to compose the two core operations: filtering out even numbers, then squaring and adding one. to compose the two core operations: filtering out even numbers, then squaring and adding one. Likewise, the 'fun x -> ...' bit of the lambda expression is also not needed, because 'x' is simply Likewise, the 'fun x -> ...' bit of the lambda expression is also not needed, because 'x' is simply being defined in that scope so that it can be passed to a functional pipeline. Thus, '>>' can be used being defined in that scope so that it can be passed to a functional pipeline. Thus, '>>' can be used there as well. there as well. The result of 'squareOddValuesAndAddOneComposition' is itself another function which takes a The result of 'squareOddValuesAndAddOneComposition' is itself another function which takes a list of integers as its input. If you execute 'squareOddValuesAndAddOneComposition' with a list list of integers as its input. If you execute 'squareOddValuesAndAddOneComposition' with a list of integers, you'll notice that it produces the same results as previous functions. of integers, you'll notice that it produces the same results as previous functions. This is using what is known as function composition. This is possible because functions in F# This is using what is known as function composition. This is possible because functions in F# use Partial Application and the input and output types of each data processing operation match use Partial Application and the input and output types of each data processing operation match the signatures of the functions we're using. the signatures of the functions we're using. Lists are ordered, immutable, singly-linked lists. They are eager in their evaluation. Lists are ordered, immutable, singly-linked lists. They are eager in their evaluation. This module shows various ways to generate lists and process lists with some functions This module shows various ways to generate lists and process lists with some functions in the 'List' module in the F# Core Library. in the 'List' module in the F# Core Library. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/lists To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/lists Lists are defined using [ ... ]. This is an empty list. Lists are defined using [ ... ]. This is an empty list. This is a list with 3 elements. ';' is used to separate elements on the same line. This is a list with 3 elements. ';' is used to separate elements on the same line. You can also separate elements by placing them on their own lines. You can also separate elements by placing them on their own lines. This is a list of integers from 1 to 1000 This is a list of integers from 1 to 1000 Lists can also be generated by computations. This is a list containing Lists can also be generated by computations. This is a list containing all the days of the year. all the days of the year. Print the first 5 elements of 'daysList' using 'List.take'. Print the first 5 elements of 'daysList' using 'List.take'. Computations can include conditionals. This is a list containing the tuples Computations can include conditionals. This is a list containing the tuples which are the coordinates of the black squares on a chess board. which are the coordinates of the black squares on a chess board. Lists can be transformed using 'List.map' and other functional programming combinators. Lists can be transformed using 'List.map' and other functional programming combinators. This definition produces a new list by squaring the numbers in numberList, using the pipeline This definition produces a new list by squaring the numbers in numberList, using the pipeline operator to pass an argument to List.map. operator to pass an argument to List.map. There are many other list combinations. The following computes the sum of the squares of the There are many other list combinations. The following computes the sum of the squares of the numbers divisible by 3. numbers divisible by 3. Arrays are fixed-size, mutable collections of elements of the same type. Arrays are fixed-size, mutable collections of elements of the same type. Although they are similar to Lists (they support enumeration and have similar combinators for data processing), Although they are similar to Lists (they support enumeration and have similar combinators for data processing), they are generally faster and support fast random access. This comes at the cost of being less safe by being mutable. they are generally faster and support fast random access. This comes at the cost of being less safe by being mutable. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/arrays To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/arrays This is The empty array. Note that the syntax is similar to that of Lists, but uses `[| ... |]` instead. This is The empty array. Note that the syntax is similar to that of Lists, but uses `[| ... |]` instead. Arrays are specified using the same range of constructs as lists. Arrays are specified using the same range of constructs as lists. This is an array of numbers from 1 to 1000. This is an array of numbers from 1 to 1000. This is an array containing only the words "hello" and "world". This is an array containing only the words "hello" and "world". This is an array initialized by index and containing the even numbers from 0 to 2000. This is an array initialized by index and containing the even numbers from 0 to 2000. Sub-arrays are extracted using slicing notation. Sub-arrays are extracted using slicing notation. You can loop over arrays and lists using 'for' loops. You can loop over arrays and lists using 'for' loops. You can modify the contents of an an array element by using the left arrow assignment operator. You can modify the contents of an an array element by using the left arrow assignment operator. To learn more about this operator, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/values/index#mutable-variables To learn more about this operator, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/values/index#mutable-variables You can transform arrays using 'Array.map' and other functional programming operations. You can transform arrays using 'Array.map' and other functional programming operations. The following calculates the sum of the lengths of the words that start with 'h'. The following calculates the sum of the lengths of the words that start with 'h'. Sequences are a logical series of elements, all of the same type. These are a more general type than Lists and Arrays. Sequences are a logical series of elements, all of the same type. These are a more general type than Lists and Arrays. Sequences are evaluated on-demand and are re-evaluated each time they are iterated. Sequences are evaluated on-demand and are re-evaluated each time they are iterated. An F# sequence is an alias for a .NET System.Collections.Generic.IEnumerable<'T>. An F# sequence is an alias for a .NET System.Collections.Generic.IEnumerable<'T>. Sequence processing functions can be applied to Lists and Arrays as well. Sequence processing functions can be applied to Lists and Arrays as well. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/sequences To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/sequences This is the empty sequence. This is the empty sequence. This a sequence of values. This a sequence of values. This is an on-demand sequence from 1 to 1000. This is an on-demand sequence from 1 to 1000. This is a sequence producing the words "hello" and "world" This is a sequence producing the words "hello" and "world" This sequence producing the even numbers up to 2000. This sequence producing the even numbers up to 2000. This is an infinite sequence which is a random walk. This is an infinite sequence which is a random walk. This example uses yield! to return each element of a subsequence. This example uses yield! to return each element of a subsequence. This example shows the first 100 elements of the random walk. This example shows the first 100 elements of the random walk. Recursive functions can call themselves. In F#, functions are only recursive Recursive functions can call themselves. In F#, functions are only recursive when declared using 'let rec'. when declared using 'let rec'. Recursion is the preferred way to process sequences or collections in F#. Recursion is the preferred way to process sequences or collections in F#. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/functions/index#recursive-functions To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/functions/index#recursive-functions This example shows a recursive function that computes the factorial of an This example shows a recursive function that computes the factorial of an integer. It uses 'let rec' to define a recursive function. integer. It uses 'let rec' to define a recursive function. Computes the greatest common factor of two integers. Computes the greatest common factor of two integers. Since all of the recursive calls are tail calls, Since all of the recursive calls are tail calls, the compiler will turn the function into a loop, the compiler will turn the function into a loop, which improves performance and reduces memory consumption. which improves performance and reduces memory consumption. This example computes the sum of a list of integers using recursion. This example computes the sum of a list of integers using recursion. This makes 'sumList' tail recursive, using a helper function with a result accumulator. This makes 'sumList' tail recursive, using a helper function with a result accumulator. This invokes the tail recursive helper function, providing '0' as a seed accumulator. This invokes the tail recursive helper function, providing '0' as a seed accumulator. An approach like this is common in F#. An approach like this is common in F#. Records are an aggregate of named values, with optional members (such as methods). Records are an aggregate of named values, with optional members (such as methods). They are immutable and have structural equality semantics. They are immutable and have structural equality semantics. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/records To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/records This example shows how to define a new record type. This example shows how to define a new record type. This example shows how to instantiate a record type. This example shows how to instantiate a record type. You can also do this on the same line with ';' separators. You can also do this on the same line with ';' separators. This example shows how to use "copy-and-update" on record values. It creates This example shows how to use "copy-and-update" on record values. It creates a new record value that is a copy of contact1, but has different values for a new record value that is a copy of contact1, but has different values for the 'Phone' and 'Verified' fields. the 'Phone' and 'Verified' fields. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/copy-and-update-record-expressions To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/copy-and-update-record-expressions This example shows how to write a function that processes a record value. This example shows how to write a function that processes a record value. It converts a 'ContactCard' object to a string. It converts a 'ContactCard' object to a string. This is an example of a Record with a member. This is an example of a Record with a member. Members can implement object-oriented members. Members can implement object-oriented members. Members are accessed via the '.' operator on an instantiated type. Members are accessed via the '.' operator on an instantiated type. Records can also be represented as structs via the 'Struct' attribute. Records can also be represented as structs via the 'Struct' attribute. This is helpful in situations where the performance of structs outweighs This is helpful in situations where the performance of structs outweighs the flexibility of reference types. the flexibility of reference types. Discriminated Unions (DU for short) are values which could be a number of named forms or cases. Discriminated Unions (DU for short) are values which could be a number of named forms or cases. Data stored in DUs can be one of several distinct values. Data stored in DUs can be one of several distinct values. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/discriminated-unions To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/discriminated-unions The following represents the suit of a playing card. The following represents the suit of a playing card. A Disciminated Union can also be used to represent the rank of a playing card. A Disciminated Union can also be used to represent the rank of a playing card. Represents the rank of cards 2 .. 10 Represents the rank of cards 2 .. 10 Discriminated Unions can also implement object-oriented members. Discriminated Unions can also implement object-oriented members. This is a record type that combines a Suit and a Rank. This is a record type that combines a Suit and a Rank. It's common to use both Records and Disciminated Unions when representing data. It's common to use both Records and Disciminated Unions when representing data. This computes a list representing all the cards in the deck. This computes a list representing all the cards in the deck. This example converts a 'Card' object to a string. This example converts a 'Card' object to a string. This example prints all the cards in a playing deck. This example prints all the cards in a playing deck. Single-case DUs are often used for domain modeling. This can buy you extra type safety Single-case DUs are often used for domain modeling. This can buy you extra type safety over primitive types such as strings and ints. over primitive types such as strings and ints. Single-case DUs cannot be implicitly converted to or from the type they wrap. Single-case DUs cannot be implicitly converted to or from the type they wrap. For example, a function which takes in an Address cannot accept a string as that input, For example, a function which takes in an Address cannot accept a string as that input, or vive/versa. or vive/versa. You can easily instantiate a single-case DU as follows. You can easily instantiate a single-case DU as follows. When you need the value, you can unwrap the underlying value with a simple function. When you need the value, you can unwrap the underlying value with a simple function. Printing single-case DUs is simple with unwrapping functions. Printing single-case DUs is simple with unwrapping functions. Disciminated Unions also support recursive definitions. Disciminated Unions also support recursive definitions. This represents a Binary Search Tree, with one case being the Empty tree, This represents a Binary Search Tree, with one case being the Empty tree, and the other being a Node with a value and two subtrees. and the other being a Node with a value and two subtrees. Check if an item exists in the binary search tree. Check if an item exists in the binary search tree. Searches recursively using Pattern Matching. Returns true if it exists; otherwise, false. Searches recursively using Pattern Matching. Returns true if it exists; otherwise, false. Check the left subtree. Check the left subtree. Check the right subtree. Check the right subtree. Inserts an item in the Binary Search Tree. Inserts an item in the Binary Search Tree. Finds the place to insert recursively using Pattern Matching, then inserts a new node. Finds the place to insert recursively using Pattern Matching, then inserts a new node. If the item is already present, it does not insert anything. If the item is already present, it does not insert anything. No need to insert, it already exists; return the node. No need to insert, it already exists; return the node. Call into left subtree. Call into left subtree. Call into right subtree. Call into right subtree. Discriminated Unions can also be represented as structs via the 'Struct' attribute. Discriminated Unions can also be represented as structs via the 'Struct' attribute. This is helpful in situations where the performance of structs outweighs This is helpful in situations where the performance of structs outweighs the flexibility of reference types. the flexibility of reference types. However, there are two important things to know when doing this: However, there are two important things to know when doing this: 1. A struct DU cannot be recursively-defined. 1. A struct DU cannot be recursively-defined. 2. A struct DU must have unique names for each of its cases. 2. A struct DU must have unique names for each of its cases. Pattern Matching is a feature of F# that allows you to utilize Patterns, Pattern Matching is a feature of F# that allows you to utilize Patterns, which are a way to compare data with a logical structure or structures, which are a way to compare data with a logical structure or structures, decompose data into constituent parts, or extract information from data in various ways. decompose data into constituent parts, or extract information from data in various ways. You can then dispatch on the "shape" of a pattern via Pattern Matching. You can then dispatch on the "shape" of a pattern via Pattern Matching. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/pattern-matching To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/pattern-matching A record for a person's first and last name A record for a person's first and last name A Discriminated Union of 3 different kinds of employees A Discriminated Union of 3 different kinds of employees Count everyone underneath the employee in the management hierarchy, Count everyone underneath the employee in the management hierarchy, including the employee. including the employee. Find all managers/executives named "Dave" who do not have any reports. Find all managers/executives named "Dave" who do not have any reports. This uses the 'function' shorthand to as a lambda expression. This uses the 'function' shorthand to as a lambda expression. [] matches an empty list. [] matches an empty list. '_' is a wildcard pattern that matches anything. '_' is a wildcard pattern that matches anything. This handles the "or else" case. This handles the "or else" case. You can also use the shorthand function construct for pattern matching, You can also use the shorthand function construct for pattern matching, which is useful when you're writing functions which make use of Partial Application. which is useful when you're writing functions which make use of Partial Application. Define some more functions which parse with the helper function. Define some more functions which parse with the helper function. Active Patterns are another powerful construct to use with pattern matching. Active Patterns are another powerful construct to use with pattern matching. They allow you to partition input data into custom forms, decomposing them at the pattern match call site. They allow you to partition input data into custom forms, decomposing them at the pattern match call site. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/active-patterns To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/active-patterns Pattern Matching via 'function' keyword and Active Patterns often looks like this. Pattern Matching via 'function' keyword and Active Patterns often looks like this. Call the printer with some different values to parse. Call the printer with some different values to parse. Option values are any kind of value tagged with either 'Some' or 'None'. Option values are any kind of value tagged with either 'Some' or 'None'. They are used extensively in F# code to represent the cases where many other They are used extensively in F# code to represent the cases where many other languages would use null references. languages would use null references. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/options To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/options First, define a zipcode defined via Single-case Discriminated Union. First, define a zipcode defined via Single-case Discriminated Union. Next, define a type where the ZipCode is optional. Next, define a type where the ZipCode is optional. Next, define an interface type that represents an object to compute the shipping zone for the customer's zip code, Next, define an interface type that represents an object to compute the shipping zone for the customer's zip code, given implementations for the 'getState' and 'getShippingZone' abstract methods. given implementations for the 'getState' and 'getShippingZone' abstract methods. Next, calculate a shipping zone for a customer using a calculator instance. Next, calculate a shipping zone for a customer using a calculator instance. This uses combinators in the Option module to allow a functional pipeline for This uses combinators in the Option module to allow a functional pipeline for transforming data with Optionals. transforming data with Optionals. Units of measure are a way to annotate primitive numeric types in a type-safe way. Units of measure are a way to annotate primitive numeric types in a type-safe way. You can then perform type-safe arithmetic on these values. You can then perform type-safe arithmetic on these values. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/units-of-measure To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/units-of-measure First, open a collection of common unit names First, open a collection of common unit names Define a unitized constant Define a unitized constant Next, define a new unit type Next, define a new unit type Conversion factor mile to meter. Conversion factor mile to meter. Define a unitized constant Define a unitized constant Compute metric-system constant Compute metric-system constant Values using Units of Measure can be used just like the primitive numeric type for things like printing. Values using Units of Measure can be used just like the primitive numeric type for things like printing. Classes are a way of defining new object types in F#, and support standard Object-oriented constructs. Classes are a way of defining new object types in F#, and support standard Object-oriented constructs. They can have a variety of members (methods, properties, events, etc.) They can have a variety of members (methods, properties, events, etc.) To learn more about Classes, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/classes To learn more about Classes, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/classes To learn more about Members, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/members To learn more about Members, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/members A simple two-dimensional Vector class. A simple two-dimensional Vector class. The class's constructor is on the first line, The class's constructor is on the first line, and takes two arguments: dx and dy, both of type 'double'. and takes two arguments: dx and dy, both of type 'double'. This internal field stores the length of the vector, computed when the This internal field stores the length of the vector, computed when the object is constructed object is constructed 'this' specifies a name for the object's self identifier. 'this' specifies a name for the object's self identifier. In instance methods, it must appear before the member name. In instance methods, it must appear before the member name. This member is a method. The previous members were properties. This member is a method. The previous members were properties. This is how you instantiate the Vector2D class. This is how you instantiate the Vector2D class. Get a new scaled vector object, without modifying the original object. Get a new scaled vector object, without modifying the original object. Generic classes allow types to be defined with respect to a set of type parameters. Generic classes allow types to be defined with respect to a set of type parameters. In the following, 'T is the type parameter for the class. In the following, 'T is the type parameter for the class. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/generics/ To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/generics/ This internal field store the states in a list. This internal field store the states in a list. Add a new element to the list of states. Add a new element to the list of states. use the '<-' operator to mutate the value. use the '<-' operator to mutate the value. Get the entire list of historical states. Get the entire list of historical states. Get the latest state. Get the latest state. An 'int' instance of the state tracker class. Note that the type parameter is inferred. An 'int' instance of the state tracker class. Note that the type parameter is inferred. Add a state Add a state Interfaces are object types with only 'abstract' members. Interfaces are object types with only 'abstract' members. Object types and object expressions can implement interfaces. Object types and object expressions can implement interfaces. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/interfaces To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/interfaces This is a type that implements IDisposable. This is a type that implements IDisposable. This is the implementation of IDisposable members. This is the implementation of IDisposable members. This is an object that implements IDisposable via an Object Expression This is an object that implements IDisposable via an Object Expression Unlike other languages such as C# or Java, a new type definition is not needed Unlike other languages such as C# or Java, a new type definition is not needed to implement an interface. to implement an interface. The FSharp.Core library defines a range of parallel processing functions. Here The FSharp.Core library defines a range of parallel processing functions. Here you use some functions for parallel processing over arrays. you use some functions for parallel processing over arrays. To learn more, see: https://msdn.microsoft.com/en-us/visualfsharpdocs/conceptual/array.parallel-module-%5Bfsharp%5D To learn more, see: https://msdn.microsoft.com/en-us/visualfsharpdocs/conceptual/array.parallel-module-%5Bfsharp%5D First, an array of inputs. First, an array of inputs. Next, define a functions that does some CPU intensive computation. Next, define a functions that does some CPU intensive computation. Next, do a parallel map over a large input array. Next, do a parallel map over a large input array. Next, print the results. Next, print the results. Events are a common idiom for .NET programming, especially with WinForms or WPF applications. Events are a common idiom for .NET programming, especially with WinForms or WPF applications. To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/members/events To learn more, see: https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/members/events First, create instance of Event object that consists of subscription point (event.Publish) and event trigger (event.Trigger). First, create instance of Event object that consists of subscription point (event.Publish) and event trigger (event.Trigger). Next, add handler to the event. Next, add handler to the event. Next, trigger the event. Next, trigger the event. Next, create an instance of Event that follows standard .NET convention: (sender, EventArgs). Next, create an instance of Event that follows standard .NET convention: (sender, EventArgs). Next, add a handler for this new event. Next, add a handler for this new event. Next, trigger this event (note that sender argument should be set). Next, trigger this event (note that sender argument should be set).