Symbol and Operator Reference (F#)

2012-08-20

This topic includes a table of symbols and operators that are used in the F# language.

Table of Symbols and Operators

The following table describes symbols used in the F# language, provides links to topics that provide more information, and provides a brief description of some of the uses of the symbol. Symbols are ordered according to the ASCII character set ordering.

Symbol or operator	Links	Description
!	Reference Cells (F#) Computation Expressions (F#)	Dereferences a reference cell. After a keyword, indicates a modified version of the keyword's behavior as controlled by a workflow.
!=	Not applicable.	Not used in F#. Use <> for inequality operations.
"	Literals (F#) Strings (F#)	Delimits a text string.
"""	Strings (F#)	Delimits a verbatim text string. Differs from @"..." in that a you can indicate a quotation mark character by using a single quote in the string.
#	Compiler Directives (F#) Flexible Types (F#)	Prefixes a preprocessor or compiler directive, such as #light. When used with a type, indicates a flexible type, which refers to a type or any one of its derived types.
$	No more information available.	Used internally for certain compiler-generated variable and function names.
%	Arithmetic Operators (F#) Code Quotations (F#)	Computes the integer modulus. Used for splicing quotations.
%?	Nullable Operators (F#)	Computes the integer modulus, when the right side is a nullable type.
&	Match Expressions (F#)	Computes the address of a mutable value, for use when interoperating with other languages. Used in AND patterns.
&&	Boolean Operators (F#)	Computes the Boolean AND operation.
&&&	Bitwise Operators (F#)	Computes the bitwise AND operation.
'	Literals (F#) Automatic Generalization (F#)	Delimits a single-character literal. Indicates a generic type parameter.
``...``	No more information available.	Delimits an identifier that would otherwise not be a legal identifier, such as a language keyword.
( )	Unit Type (F#)	Represents the single value of the unit type.
(...)	Tuples (F#) Operator Overloading (F#)	Indicates the order in which expressions are evaluated. Delimits a tuple. Used in operator definitions.
(...)		Delimits a comment that could span multiple lines.
(\|...\|)	Active Patterns (F#)	Delimits an active pattern. Also called banana clips.
*	Arithmetic Operators (F#) Tuples (F#) Units of Measure (F#)	When used as a binary operator, multiplies the left and right sides. In types, indicates pairing in a tuple. Used in units of measure types.
*?	Nullable Operators (F#)	Multiplies the left and right sides, when the right side is a nullable type.
**	Arithmetic Operators (F#)	Computes the exponentiation operation (x ** y means x to the power of y).
+	Arithmetic Operators (F#)	When used as a binary operator, adds the left and right sides. When used as a unary operator, indicates a positive quantity. (Formally, it produces the same value with the sign unchanged.)
+?	Nullable Operators (F#)	Adds the left and right sides, when the right side is a nullable type.
,	Tuples (F#)	Separates the elements of a tuple, or type parameters.
-	Arithmetic Operators (F#)	When used as a binary operator, subtracts the right side from the left side. When used as a unary operator, performs a negation operation.
-	Nullable Operators (F#)	Subtracts the right side from the left side, when the right side is a nullable type.
->	Functions (F#) Match Expressions (F#)	In function types, delimits arguments and return values. Yields an expression (in sequence expressions); equivalent to the yield keyword. Used in match expressions
.	Members (F#) Primitive Types (F#)	Accesses a member, and separates individual names in a fully qualified name. Specifies a decimal point in floating point numbers.
..	Loops: for...in Expression (F#)	Specifies a range.
.. ..	Loops: for...in Expression (F#)	Specifies a range together with an increment.
.[...]	Arrays (F#)	Accesses an array element.
/	Arithmetic Operators (F#) Units of Measure (F#)	Divides the left side (numerator) by the right side (denominator). Used in units of measure types.
/?	Nullable Operators (F#)	Divides the left side by the right side, when the right side is a nullable type.
//		Indicates the beginning of a single-line comment.
///	XML Documentation (F#)	Indicates an XML comment.
:	Functions (F#)	In a type annotation, separates a parameter or member name from its type.
::	Lists (F#) Match Expressions (F#)	Creates a list. The element on the left side is appended to the list on the right side. Used in pattern matching to separate the parts of a list.
:=	Reference Cells (F#)	Assigns a value to a reference cell.
:>	Casting and Conversions (F#)	Converts a type to type that is higher in the hierarchy.
:?	Match Expressions (F#)	Returns true if the value matches the specified type; otherwise, returns false (type test operator).
:?>	Casting and Conversions (F#)	Converts a type to a type that is lower in the hierarchy.
;	Verbose Syntax (F#) Lists (F#) Records (F#)	Separates expressions (used mostly in verbose syntax). Separates elements of a list. Separates fields of a record.
<	Arithmetic Operators (F#)	Computes the less-than operation.
<?	Nullable Operators (F#)	Computes the less than operation, when the right side is a nullable type.
<<	Functions (F#)	Composes two functions in reverse order; the second one is executed first (backward composition operator).
<<<	Bitwise Operators (F#)	Shifts bits in the quantity on the left side to the left by the number of bits specified on the right side.
<-	Values (F#)	Assigns a value to a variable.
<...>	Automatic Generalization (F#)	Delimits type parameters.
<>	Arithmetic Operators (F#)	Returns true if the left side is not equal to the right side; otherwise, returns false.
<>?	Nullable Operators (F#)	Computes the "not equal" operation when the right side is a nullable type.
<=	Arithmetic Operators (F#)	Returns true if the left side is less than or equal to the right side; otherwise, returns false.
<=?	Nullable Operators (F#)	Computes the "less than or equal to" operation when the right side is a nullable type.
<\|	Functions (F#)	Passes the result of the expression on the right side to the function on left side (backward pipe operator).
<\|\|	Operators.( <\|\| )<'T1,'T2,'U> Function (F#)	Passes the tuple of two arguments on the right side to the function on left side.
<\|\|\|	Operators.( <\|\|\| )<'T1,'T2,'T3,'U> Function (F#)	Passes the tuple of three arguments on the right side to the function on left side.
<@...@>	Code Quotations (F#)	Delimits a typed code quotation.
<@@...@@>	Code Quotations (F#)	Delimits an untyped code quotation.
=	Arithmetic Operators (F#)	Returns true if the left side is equal to the right side; otherwise, returns false.
=?	Nullable Operators (F#)	Computes the "equal" operation when the right side is a nullable type.
==	Not applicable.	Not used in F#. Use = for equality operations.
>	Arithmetic Operators (F#)	Returns true if the left side is greater than the right side; otherwise, returns false.
>?	Nullable Operators (F#)	Computes the "greather than" operation when the right side is a nullable type.
>>	Functions (F#)	Composes two functions (forward composition operator).
>>>	Bitwise Operators (F#)	Shifts bits in the quantity on the left side to the right by the number of places specified on the right side.
>=	Arithmetic Operators (F#)	Returns true if the right side is greater than or equal to the left side; otherwise, returns false.
>=?	Nullable Operators (F#)	Computes the "greater than or equal" operation when the right side is a nullable type.
?	Parameters and Arguments (F#)	Specifies an optional argument. Used as an operator for dynamic method and property calls. You must provide your own implementation.
? ... <- ...	No more information available.	Used as an operator for setting dynamic properties. You must provide your own implementation.
?>=, ?>, ?<=, ?<, ?=, ?<>, ?+, ?-, ?*, ?/	Nullable Operators (F#)	Equivalent to the corresponding operators without the ? prefix, where a nullable type is on the left.
>=?, >?, <=?, <?, =?, <>?, +?, -?, *?, /?	Nullable Operators (F#)	Equivalent to the corresponding operators without the ? suffix, where a nullable type is on the right.
?>=?, ?>?, ?<=?, ?<?, ?=?, ?<>?, ?+?, ?-?, ?*?, ?/?	Nullable Operators (F#)	Equivalent to the corresponding operators without the surrounding question marks, where both sides are nullable types.
@	Lists (F#) Strings (F#)	Concatenates two lists. When placed before a string literal, indicates that the string is to be interpreted verbatim, with no interpretation of escape characters.
[...]	Lists (F#)	Delimits the elements of a list.
[\|...\|]	Arrays (F#)	Delimits the elements of an array.
[<...>]	Attributes (F#)	Delimits an attribute.
\	Strings (F#)	Escapes the next character; used in character and string literals.
^	Statically Resolved Type Parameters (F#) Strings (F#)	Specifies type parameters that must be resolved at compile time, not at runtime. Concatenates strings.
^^^	Bitwise Operators (F#)	Computes the bitwise exclusive OR operation.
_	Match Expressions (F#) Generics (F#)	Indicates a wildcard pattern. Specifies an anonymous generic parameter.
`	Automatic Generalization (F#)	Used internally to indicate a generic type parameter.
{...}	Sequences (F#) Records (F#)	Delimits sequence expressions and computation expressions. Used in record definitions.
\|	Match Expressions (F#)	Delimits individual match cases, individual discriminated union cases, and enumeration values.
\|\|	Boolean Operators (F#)	Computes the Boolean OR operation.
\|\|\|	Bitwise Operators (F#)	Computes the bitwise OR operation.
\|>	Functions (F#)	Passes the result of the left side to the function on the right side (forward pipe operator).
\|\|>	Operators.( \|\|> )<'T1,'T2,'U> Function (F#)	Passes the tuple of two arguments on the left side to the function on the right side.
\|\|\|>	Operators.( \|\|\|> )<'T1,'T2,'T3,'U> Function (F#)	Passes the tuple of three arguments on the left side to the function on the right side.
~~	Operator Overloading (F#)	Used to declare an overload for the unary negation operator.
~~~	Bitwise Operators (F#)	Computes the bitwise NOT operation.
~-	Operator Overloading (F#)	Used to declare an overload for the unary minus operator.
~+	Operator Overloading (F#)	Used to declare an overload for the unary plus operator.

Operator Precedence

The following table shows the order of precedence of operators and other expression keywords in the F# language, in order from lowest precedence to the highest precedence. Also listed is the associativity, if applicable.

Operator	Associativity
as	Right
when	Right
\| (pipe)	Left
;	Right
let	Nonassociative
function, fun, match, try	Nonassociative
if	Nonassociative
->	Right
:=	Right
,	Nonassociative
or, \|\|	Left
&, &&	Left
<op, >op, =, \|op, &op	Left
&&&, \|\|\|, ^^^, ~~~, <<<, >>>	Left
^op	Right
::	Right
:?>, :?	Nonassociative
-op, +op, (binary)	Left
*op, /op, %op	Left
**op	Right
f x (function application)	Left
\| (pattern match)	Right
prefix operators (+op, -op, %, %%, &, &&, !op, ~op)	Left
.	Left
f(x)	Left
f<types>	Left

F# supports custom operator overloading. This means that you can define your own operators. In the previous table, op can be any valid (possibly empty) sequence of operator characters, either built-in or user-defined. Thus, you can use this table to determine what sequence of characters to use for a custom operator to achieve the desired level of precedence. Leading . characters are ignored when the compiler determines precedence.

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Symbol and Operator Reference (F#)

Table of Symbols and Operators

Operator Precedence

See Also

Reference

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