Example

Racket	C++
(define square (lambda (x) (* x x)))	double square(double x) { return x * x; }

• The keyword double specifies a type, namely a double precision floating point number
  • First use: the type of the function's return value
  • Second use: the type of the function's argument x
• The keyword return specifies the function's return value;
  if you forget it the function will return a null value.