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Pm_tut> :t negate
negate :: Num a => a -> a

Pm_tut> :t (-)
(-) :: Num a => a -> a -> a

nats = [0..]

Pm_tut> take 10 nats
[0,1,2,3,4,5,6,7,8,9]

open FH, '<', $file or die "Can't open $file for reading: $!\n";

const x y = x

(-) :: Num a => a -> a -> a

(-) :: Num a => (a, a) -> a

(-) :: Num a => a -> (a -> a)

(5-)

Pm_tut> putStr "Hello, world!\n"
Hello, world!

Pm_tut>

factorial n = if n == 0 then 1
                else n * factorial (n-1)

Pm_tut> :t factorial
factorial :: Num a => a -> a

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

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

factorial 0     = 1
factorial (n+1) = (n+1) * factorial n

factorial n = tr n 1 where
    tr 0 f = f
    tr n f = tr (n-1) (n*f)

factorial n = product [1..n]

product = foldl (*) 1

foldl f z []     =  z
foldl f z (x:xs) =  foldl f (f z x) xs

product xs = foldl (*) 1 xs

sum xs = foldl (+) 0 xs        -- this is in the Standard Prelude, too

or xs = foldl (||) False xs   -- this is also in the Prelude

and xs = foldl (&&) True xs    -- so is this

anyprime xs = or (map prime xs)  -- map does what you'd expect
allprime xs = and (map prime xs)

foldl :: (a -> b -> a) -> a -> [b] -> a

andprime p n = p && prime n
allprime xs  = foldl andprime True xs

allprime xs = foldl (\p n -> p && prime n) True xs

factorials = scanl (*) 1 [1..]

Pm_tut> take 10 factorials
[1,1,2,6,24,120,720,5040,40320,362880]
Pm_tut> factorials !! 24
620448401733239439360000

Pm_tut> factorials !! 65536

ERROR - Garbage collection fails to reclaim sufficient space
Pm_tut>