(ALGOL 60)
comment I have written the following simple routine, which may separate the "man-compilers" from the "boy-compilers" - D. E. Knuth.
comment Original ALGOL 60 program by Knuth, different values obtained by modifying the "10" in the last line.
begin
real procedure A (k, x1, x2, x3, x4, x5);
value k; integer k;
begin
real procedure B;
begin k:= k - 1;
B:= A := A (k, B, x1, x2, x3, x4);
end;
if k <= 0 then A:= x4 + x5 else B;
end;
outreal (A (10, 1, -1, -1, 1, 0));
end;
Smalltalk:
Integer>>manOrBoy
^self x1: [1] x2: [-1] x3: [-1] x4: [1] x5: [0]
Integer>>x1: x1 x2: x2 x3: x3 x4: x4 x5: x5
| b k |
k := self.
b := [ k := k - 1. k x1: b x2: x1 x3: x2 x4: x3 x5: x4 ].
^k <= 0 ifTrue: [ x4 value + x5 value ] ifFalse: b
Example: '10 manOrBoy' returns -67
(C++)
#include <functional>
#include <iostream>
using cf = std::function<int()>;
int A(int k, cf x1, cf x2, cf x3, cf x4, cf x5)
{
int Aval;
cf B = [&]()
{
int Bval;
--k;
Bval = Aval = A(k, B, x1, x2, x3, x4);
return Bval;
};
if (k <= 0) Aval = x4() + x5(); else B();
return Aval;
}
cf I(int n) { return [=](){ return n; }; }
int main()
{
for (int n=0; n<10; ++n)
std::cout << A(n, I(1), I(-1), I(-1), I(1), I(0)) << ", ";
std::cout << std::endl;
(PARI) Vec(O(x^66)+(2*x^9-11*x^8+15*x^7+x^6-16*x^5+13*x^4+x^3-8*x^2+5*x-1)/((x-1)*(x^4-5*x^3+6*x^2-4*x+1))) \\
Joerg Arndt, Jul 21 2013
