Note
Access to this page requires authorization. You can try signing in or changing directories.
Access to this page requires authorization. You can try changing directories.
This topic contains links to information about all F# language keywords.
F# Keyword Table
The following table shows all F# keywords in alphabetical order, together with brief descriptions and links to relevant topics that contain more information.
Keyword |
Link |
Description |
|---|---|---|
abstract |
Indicates a method that either has no implementation in the type in which it is declared or that is virtual and has a default implementation. |
|
and |
Used in mutually recursive bindings, in property declarations, and with multiple constraints on generic parameters. |
|
as |
Used to give the current class object an object name. Also used to give a name to a whole pattern within a pattern match. |
|
assert |
Used to verify code during debugging. |
|
base |
Used as the name of the base class object. |
|
begin |
In verbose syntax, indicates the start of a code block. |
|
class |
In verbose syntax, indicates the start of a class definition. |
|
default |
Indicates an implementation of an abstract method; used together with an abstract method declaration to create a virtual method. |
|
delegate |
Used to declare a delegate. |
|
do |
Loops: for...to Expression (F#) |
Used in looping constructs or to execute imperative code. |
done |
In verbose syntax, indicates the end of a block of code in a looping expression. |
|
downcast |
Used to convert to a type that is lower in the inheritance chain. |
|
downto |
In a for expression, used when counting in reverse. |
|
elif |
Used in conditional branching. A short form of else if. |
|
else |
Used in conditional branching. |
|
end |
In type definitions and type extensions, indicates the end of a section of member definitions. In verbose syntax, used to specify the end of a code block that starts with the begin keyword. |
|
exception |
Used to declare an exception type. |
|
extern |
Indicates that a declared program element is defined in another binary or assembly. |
|
false |
Used as a Boolean literal. |
|
finally |
Used together with try to introduce a block of code that executes regardless of whether an exception occurs. |
|
for |
Used in looping constructs. |
|
fun |
Used in lambda expressions, also known as anonymous functions. |
|
function |
Used as a shorter alternative to the fun keyword and a match expression in a lambda expression that has pattern matching on a single argument. |
|
global |
Used to reference the top-level .NET namespace. |
|
if |
Used in conditional branching constructs. |
|
in |
Used for sequence expressions and, in verbose syntax, to separate expressions from bindings. |
|
inherit |
Used to specify a base class or base interface. |
|
inline |
Used to indicate a function that should be integrated directly into the caller's code. |
|
interface |
Used to declare and implement interfaces. |
|
internal |
Used to specify that a member is visible inside an assembly but not outside it. |
|
lazy |
Used to specify a computation that is to be performed only when a result is needed. |
|
let |
Used to associate, or bind, a name to a value or function. |
|
match |
Used to branch by comparing a value to a pattern. |
|
member |
Used to declare a property or method in an object type. |
|
module |
Used to associate a name with a group of related types, values, and functions, to logically separate it from other code. |
|
mutable |
Used to declare a variable, that is, a value that can be changed. |
|
namespace |
Used to associate a name with a group of related types and modules, to logically separate it from other code. |
|
new |
Used to declare, define, or invoke a constructor that creates or that can create an object. Also used in generic parameter constraints to indicate that a type must have a certain constructor. |
|
not |
Not actually a keyword. However, not struct in combination is used as a generic parameter constraint. |
|
null |
Indicates the absence of an object. Also used in generic parameter constraints. |
|
of |
Used in discriminated unions to indicate the type of categories of values, and in delegate and exception declarations. |
|
open |
Used to make the contents of a namespace or module available without qualification. |
|
or |
Used with Boolean conditions as a Boolean or operator. Equivalent to ||. Also used in member constraints. |
|
override |
Used to implement a version of an abstract or virtual method that differs from the base version. |
|
private |
Restricts access to a member to code in the same type or module. |
|
public |
Allows access to a member from outside the type. |
|
rec |
Used to indicate that a function is recursive. |
|
return |
Used to indicate a value to provide as the result of a computation expression. |
|
static |
Used to indicate a method or property that can be called without an instance of a type, or a value member that is shared among all instances of a type. |
|
struct |
Used to declare a structure type. Also used in generic parameter constraints. Used for OCaml compatibility in module definitions. |
|
then |
Used in conditional expressions. Also used to perform side effects after object construction. |
|
to |
Used in for loops to indicate a range. |
|
true |
Used as a Boolean literal. |
|
try |
Used to introduce a block of code that might generate an exception. Used together with with or finally. |
|
type |
Used to declare a class, record, structure, discriminated union, enumeration type, unit of measure, or type abbreviation. |
|
upcast |
Used to convert to a type that is higher in the inheritance chain. |
|
use |
Used instead of let for values that require Dispose to be called to free resources. |
|
val |
Used in a signature to indicate a value, or in a type to declare a member, in limited situations. |
|
void |
Indicates the .NET void type. Used when interoperating with other .NET languages. |
|
when |
Used for Boolean conditions (when guards) on pattern matches and to introduce a constraint clause for a generic type parameter. |
|
while |
Introduces a looping construct. |
|
with |
Used together with the match keyword in pattern matching expressions. Also used in object expressions, record copying expressions, and type extensions to introduce member definitions, and to introduce exception handlers. |
|
yield |
Used in a sequence expression to produce a value for a sequence. |
In addition, the following tokens are reserved in F# because they are keywords in the OCaml language:
asr |
land |
lor |
lsl |
lsr |
lxor |
mod |
sig |
If you use the --mlcompatibility compiler option, these keywords are available for use as identifiers.
The following tokens are reserved as keywords for future expansion of the F# language:
atomic |
break |
checked |
component |
const |
constraint |
constructor |
continue |
eager |
event |
external |
fixed |
functor |
include |
method |
mixin |
object |
parallel |
process |
protected |
pure |
sealed |
tailcall |
trait |
virtual |
volatile |
See Also
Reference
Symbol and Operator Reference (F#)