$_ localization in map:

my @fn_refs = map {sub { print "$_\n"}} qw(foo bar baz); for (@fn_refs) { $_->(); }
CODE(0x8105f9c) CODE(0x8105f9c) CODE(0x8105f9c)
my @fn_refs = map {my $x=$_; sub { print "$x\n"}} qw(foo bar baz); for (@fn_refs) { $_->(); }
foo bar baz
$_ doesn't get localized to the codeblock in this call to map; assign to a local var first.

Sieve of Eratosthenes in Haskell:

sieve :: [Int] -> [Int] -> [Int] -- sieve [] xs -- Assuming that xs is a list of the form [2..max], returns a list of -- primes between 2 and max. The first parameter is an accumulator -- list. -- -- This is a loose interpretation of the Sieve of Eratosthenes; instea +d -- of marking composite numbers, we remove them. sieve p [] = reverse p sieve p (x:xs) = sieve (x:p) (filter (\t -> (rem t x /= 0)) xs)

More pattern matching in Haskell:

factorial n | n == 0 = 1 | otherwise = n * factorial (n-1)

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