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Verbose Syntax

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There are two forms of syntax available for many constructs in F#: verbose syntax and lightweight syntax. The verbose syntax is not as commonly used, but has the advantage of being less sensitive to indentation. The lightweight syntax is shorter and uses indentation to signal the beginning and end of constructs, rather than additional keywords like begin, end, in, and so on. The default syntax is the lightweight syntax. This topic describes the syntax for F# constructs when lightweight syntax is not enabled. Verbose syntax is always enabled, so even if you enable lightweight syntax, you can still use verbose syntax for some constructs.

Table of Constructs

The following table shows the lightweight and verbose syntax for F# language constructs in contexts where there is a difference between the two forms. In this table, angle brackets (<>) enclose user-supplied syntax elements. Refer to the documentation for each language construct for more detailed information about the syntax used within these constructs.

Language construct Lightweight syntax Verbose syntax
compound expressions 
<expression1>
<expression2>

<expression1>; <expression2>

nested let bindings

 
let f x =
    let a = 1
    let b = 2
    x + a + b

let f x =
    let a = 1 in
    let b = 2 in
    x + a + b
code block 
(
    <expression1>
    <expression2>
)

begin
    <expression1>;
    <expression2>;
end
`for...do` 
for counter = start to finish do
    ...

for counter = start to finish do
    ...
done
`while...do` 
while <condition> do
    ...

while <condition> do
    ...
done
`for...in` 
for var in start .. finish do
    ...

for var in start .. finish do
    ...
done
`do` 
do
    ...

do
    ...
in
record 
type <record-name> =
    {
        <field-declarations>
    }
    <value-or-member-definitions>

type <record-name> =
    {
        <field-declarations>
    }
    with
        <value-or-member-definitions>
    end
class 
type <class-name>(<params>) =
    ...

type <class-name>(<params>) =
    class
        ...
    end
structure 
[<StructAttribute>]
type <structure-name> =
    ...

type <structure-name> =
    struct
        ...
    end
discriminated union 
type <union-name> =
    | ...
    | ...
    ...
    <value-or-member definitions>

type <union-name> =
    | ...
    | ...
    ...
    with
        <value-or-member-definitions>
    end
interface 
type <interface-name> =
    ...

type <interface-name> =
    interface
        ...
    end
object expression 
{ new <type-name>
    with
        <value-or-member-definitions>
        <interface-implementations>
}

{ new <type-name>
    with
        <value-or-member-definitions>
    end
    <interface-implementations>
}
interface implementation 
interface <interface-name>
    with
        <value-or-member-definitions>

interface <interface-name>
    with
        <value-or-member-definitions>
    end
type extension 
type <type-name>
    with
        <value-or-member-definitions>

type <type-name>
    with
        <value-or-member-definitions>
    end
module 
module <module-name> =
    ...

module <module-name> =
    begin
        ...
    end

See also