How this function returns "hello there"? There is definitely something that I am missing here but I don't see it

def saySomething(prefix: String) = (s: String) => {  
prefix   " "   s
} 

def saySomethingElse = saySomething("hello")

print(saySomethingElse("there"))

I tried tracing how "hello" is substituted by prefix since its the first string being passed in the function "saySomething" but then I don't understand how "there" is attached to the result.

Any help is appreciated

CodePudding user response：

Breaking it down, it works like this:

def saySomething(prefix: String) = (s: String) => {  
  prefix   " "   s
} 

This is a function called saySomething that returns a value:

def saySomething(prefix: String) = ???

The value it returns is an anonymous function:

(s: String) => { prefix   " "   s } 

Each time you call saySomething(prefix: String), a new function is created and the value of prefix is remembered by that new function. So when you call saySomething("hello") it remembers "hello" and returns this.

(s: String) => { "hello"   " "   s } 
def saySomethingElse = (s: String) => { "hello"   " "   s } 

When you call that new function, you get the final string:

saySomethingElse("there")
// == ((s: String) => { "hello"   " "   s })("there")
// == "hello"   " "   "there"

You could call it with a different value and get a different result:

saySomethingElse("Dolly")
// == ((s: String) => { "hello"   " "   s })("Dolly")
// == "hello"   " "   "Dolly"

Note that saySomethingElse can just be a val not a def. It is just a variable that contains a function, it doesn't need to be a function itself.