About pipes, curry and partial application

autocurry.fsx

// The following example shows an effect of auto-currying in fsharp.

let add x y = x + y
let substract x y = x - y 

// So that could look like a totally viable definition to you. 
// We define an add, and a substract function for later use. 
// But now watch. 

let calculate = 
  10
  |> add 2 
  |> substract 2
  
// What do you think, does come out of that?
// You could think, 10 pipes into `add 2`, that makes 12. 
// And then, 12 pipes into `substract 2`, and that makes 10. 

val calculate: int = -10

// So no. Its -10. Why is that? 

// Because pipes are gentle. 
// See for yourself;

let calculate = 
    10 
    |> add 2 // add 2 10 = 12
    |> subtract 2 // subtract 2 12 = -10

// It actually goes this way. ^
// The value gets set on the first open position, reading left to right. 

// In this case, its the open "y" position of the add function. 
// `add` applies 2 at first to its x position. Then only comes the value from the pipe.