I do not understand the following program code. Can anyone explain it to me?
(define myFunction
(lambda (f x y z)
(f x y z)))
How can I simplify it?
1
votes
2 Answers
4
votes
You can't simplify it much, except for making it look a bit syntactic, as
(define (myFunction f x y z)
(f x y z))
which is a syntactic shortcut for defining the exact same thing.
This way, you can treat it mentally as a rewriting rule: whenever you see
(myFunction f x y z)
in your code - whatever those f, x, y and z placeholders are referring to - you can replace it with
(f x y z)
while substituting the actual values, a.k.a. arguments, for the placeholders, a.k.a. function parameters.
Thus you see that for the new code to make sense, f should be a function capable of accepting three arguments, x, y and z.
So for example, if you define (define (f x y z) (+ x y z)), you can call
(myFunction f 1 2 3)
and get a result back - which is the result of calling the function f you've just defined above, with the values 1, 2 and 3.
f inside myFunction will refer to the global name f which refers to a value - a function named f you've defined. The lambda form defines a value - an anonymous function - and define binds a name f to it, so that any use of that name refers to that value, from now on. In Scheme, functions are values like any other.
That global function f is defined to apply + to the three arguments it receives, when it receives them. It in effect is saying, "give me some three values and I'll sum them up for you", and the call (myFunction f 1 2 3) supplies it with the three values of your choosing.
