Besides the primitive types, the F# library includes several core types that will allow you to organize, manipulate and process data.
Unit
The unit type is a value signifying nothing of consequence. unit can be thought of as a concrete representation of void and is represented in code via ():
> let x=();;
val x : unit=()
> x;;
val it : unit()
if expressions without a matching else must return unit because if they did return a value, what would happen if else was hit?
Also, in F#, every function must return a value, think method in C# and the void return type, so even if the function doesn’t conceptually return anything, then it should return a unit value.
The ignore function can swallow a function’s return value if you want to return unit:
> let square x=x*x;;
val square :int->int
> ignore (square 3);;
val it : unit=()
Tuple
A tuple (pronounced two-pull) is an ordered collection of data,easy way to group common pieces of data together. For example, tuples can be used to track the intermediate results of a computation.
To create an instance of a tuple, separate group of values with comma, and optionally place them within parentheses. Let's have fullName as an instance of a tuple, while string * string is the tuples type:
> let fullName = ("ganesan", "senthilvel");;
val fullName : string * string = ("ganesan", "senthilvel")
Tuples can contain any number of values of any type. You can have a tuple that contains other tuples.
