Man Or Boy
September 16, 2016
During the development of Algol 60, Donald Knuth devised a nasty test of recursion:
There are quite a few ALGOL60 translators in existence which have been designed to handle recursion and non-local references properly, and I thought perhaps a little test-program may be of value. Hence I have written the following simple routine, which may separate the man-compilers from the boy-compilers: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 ≤ then A : = x4 + x5 else B end outreal(A(10, 1, -1, -1, 1, 0)) end
This uses nothing known to be tricky or ambiguous. My question is: What should the answer be? Unfortunately, I don’t have to a man-compiler myself, and so I was forced to try hand calculations. My conjecture (probably wrong) is that the answer will be:73 - 119 - 177 + 102 = - 121
I’d be very glad to know the right answer.
Your task is to write a program that computes the right answer. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.
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