Import Declarations: The open keyword
An import declaration specifies a module or namespace. You can reference it's elements without using a fully qualified name.
F# allows you to use the open keyword for frequently used modules and namespaces. When you reference a member of frequently used module or namespace, you can use the short form of the name instead of the fully qualified name. This open keyword is similar to the using keyword in C#, and Imports in Visual Basic.
When you use multiple open declarations, they should appear on separate lines.
F# Import declaration Example
Hello, this is F# here.
Namespaces That Are import by Default in F#
In F#, some namespaces that are used most frequently is open by default. These namespaces are listed below in the table.