// A function definition.

f(x, y) = x^2 + 3*y

// Various syntax for function application.

f(3, 4)   // Math, C, Java, JavaScript

f 3 4     // ML, F#, Haskell

(f 3 4)   // Lisp, Scheme, Clojure (a tree)

     f
    / \
   3   4
   
(+ 3 4)  // a tree
    
     +
    / \
   3   4

(apply f 3 4)  // Language_7

     apply
    /  |  \
   f   3   4


A function with no arguments.

g() = 5    // function definition

// syntax for function application (function call)

g()        // Math, Java, C
g          // ML, F#, Haskell
(g)        // Lisp, not really a tree
(apply g)  // Language_7 (a tree)

      apply
        |
        g