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# mode: run
# tag: closures
# Cython version of Knuth's "man or boy" test -- "It separates the man
# Algol 60 compilers from the boy Algol 60 compilers." Here's the
# original (from wikipedia):
#
# 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;
#
# and a table of values:
#
# k A
# 0 1
# 1 0
# 2 -2
# 3 0
# 4 1
# 5 0
# 6 1
# 7 -1
# 8 -10
# 9 -30
# 10 -67
#
# Past 10 or so, we blow the C stack -- can't just set a higher recursion limit
# to get around that one.
#
def compute(val):
if isinstance(val, int):
return val
else:
return val()
def a(in_k, x1, x2, x3, x4, x5):
"""
>>> import sys
>>> old_limit = sys.getrecursionlimit()
>>> sys.setrecursionlimit(1350 if not getattr(sys, 'pypy_version_info', None) else 2700)
>>> a(10, 1, -1, -1, 1, 0)
-67
>>> sys.setrecursionlimit(old_limit)
"""
k = [in_k]
def b():
k[0] -= 1
return a(k[0], b, x1, x2, x3, x4)
return compute(x4) + compute(x5) if k[0] <= 0 else b()
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