FoxtrotUniform's scratchpad

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$_ localization in map:

my @fn_refs = map {sub { print "$_\n"}} qw(foo bar baz);

for (@fn_refs) {
    $_->();
}
[download]

produces

CODE(0x8105f9c)
CODE(0x8105f9c)
CODE(0x8105f9c)
[download]

but

my @fn_refs = map {my $x=$_; sub { print "$x\n"}} qw(foo bar baz);

for (@fn_refs) {
    $_->();
}
[download]

produces

foo
bar
baz
[download]

$_ 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)
[download]

More pattern matching in Haskell:

factorial n
  | n == 0    = 1
  | otherwise = n * factorial (n-1)
[download]

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