Name Recipes/Basic/Factorial

Synopsis Compute the factorial function.

Examples The factorial of a number N is defined as N * (N-1) * (N-2) * ... * 1. Here is the Rascal version:

module demo::basic::Factorial

public int fac(int N) = N <= 0 ? 1 : N * fac(N - 1); 

public int fac2(0) = 1; 
public default int fac2(int N) = N * fac2(N - 1); 

public int fac3(int N)  { 
  if (N == 0) 
    return 1;
  return N * fac3(N - 1);
}

Implementation uses a conditional expression to distinguish cases and here is how to use it:

rascal>import demo::basic::Factorial;
ok
rascal>fac(47);
int: 258623241511168180642964355153611979969197632389120000000000

Indeed, Rascal has arbitrary length integers.

Definitions and do the same using pattern dispatch (Rascal:Function):

rascal>import demo::basic::Factorial;
ok
rascal>fac2(47);
int: 258623241511168180642964355153611979969197632389120000000000

Definition is a more imperative implementation of factorial.

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