On 09/12/2011 01:36 PM, bearophile wrote:
It seems people (Andrei too) are slowly adding more comments in that Reddit
thread.
A sub-thread:
http://www.reddit.com/r/programming/comments/kaxjq/the_d_programming_language_is_back_in_tiobes_top/c2iycwb
It starts with this question:
How would you write this kind of Python in D?
from struct import Struct
def decode(buf):
while buf:
s = Struct(buf[0])
val, = s.unpack(buf[1 : 1 + s.size])
yield val
buf = buf[1 + s.size:]
Or this:
def powerset(items):
if not items:
yield []
return
item, rest = items[0], items[1:]
for opt in [[item], []]:
for r in powerset(rest):
yield opt + r
btw, I like Haskell even more, and in it, the latter example is:
powerset [] = return []
powerset (x:xs) = do
o<- [[x], []]
r<- powerset xs
return $ o ++ r
Or, you can re-use the filterM function, and get:
powerset = filterM (\x -> [True,False])
Equivalent D version. Runs in ca 22 min on my machine (for computing the
size of P(Z_21))
LList!(List!T) powerset(T)(Lazy!(List!T) xs){
return lz({
if(xs().empty) return list(Empty!T)();
auto r=lz({return powerset(xs().tail)();});
return chain(r,map((LList!T a){return
cons(xs().head,a);},r))();
});
}
writeln(powerset(take(21,naturals(0))).length);
2097152
real 21m58.438s
user 21m32.320s
sys 0m4.710s
