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Using procedures in Icon

Suppose you need to compute the factorial function, N! = 1 * 2 * ... * N. Here's a complete Icon program containing a procedure that computes the factorial function, and a main program that prints all the values up to 4:

procedure main ( )
  every  n := 1 to 4  do
    write ( n, "! = ", Factorial ( n ) );
end

procedure Factorial ( k )        # Returns k! = 1*2*...*k
  result  :=  1;                 # Prepare to compute product
  every  result *:= ( 1 to k );  # Multiply by 1, 2, ..., k
  return result;
end

1! = 1
2! = 2
3! = 6
4! = 24