f# essential - part 11 - ignore function

If you call a function which does not return unit type, you can not call it like the following.

let f1() = 
    //do some side effect stuff
    "f1"
f1()

You have to do the following

f1() |> ignore
//or 
let _ = f1()

f# essential - part 10 - why and when f# does not need null value,

I am surprise when I don't see a need to use null in f#. It use a generic record type "option", which is a very elegant solution to express nullness. In c#, we have reference type and value type, in .net 1/1.1, we express nullness for reference type using "null", in .net 2 above, we can use Nullable type of value type. However, f# unify this using option.

The null keyword is a valid keyword in the F# language, and you have to use it when you are working with .NET Framework APIs or other APIs that are written in another .NET language. The two situations in which you might need a null value are when you call a .NET API and pass a null value as an argument, and when you interpret the return value or an output parameter from a .NET method call. For more please refer to MSDN

f# essential - part 9 - no need to use ref record type in class

As I discussed it in post f# essential - part 5 - mutable, ref, ref record is used for closure. And mutable is similar concept of variable in c#. So that you can not use mutable defined outside of a function. So the following it is wrong

let build_t() = 
    let mutable x = 0
    let t() =
        x <- 1 + x
        printfn "you call me %i time(s)" x
    t

f# essential - part 8 - talking to c# library

When I found that syntax in f# to support curry, I am very excited. May be we can do the same thing with .net library written in c#. For example, maybe I can use Console.WriteLine as a function to write the following code.

let greet = Console.WriteLine "hello, {0}"
greet "fred"
Console.WriteLine "hello, {0}" "fred"

The compiler give me an error "The value is not a function and can not be applied". So F# function is different from c# method. To call this method, you have to use a tuple syntax. But you can wrap a method easily into a f# function, then you can do curry

Console.WriteLine ("hello, {0}", "fred")

f# essential - part 7 Curry

Function application, also sometimes referred to as function composition or composing functions is a big thing in functional programming. One style of composition is called Curry. Curry is feature of lots functional language. When you have a function with two parameter, you can pass one argument to the function, that create an new partial function, which accept one parameter. This partial function is also called curried function. F# support this in a very elegant syntax.

let print x y = 
     printfn "%i" x 
     printfn "%s" y 
let print100y = print 100 //create a curried function 
print100y "hello" //call the curried function 

If you want to fill in the second argument to create a new function, this is also support, like below.

let printx_hello x = dosomething x "hello" 
printx_hello 100