-- function
tadd a b = a+b
tmax a b = if a > b then a else b
-- declaration
tdefinition = "function can be used as constant with no argument, note that functionname always start with lower case letter"
tconstant = "in ghci you can define function/constant/def using ' ghci> let ... = .... \
           \ also it is possible to have multiline string this way "
-- list
tlistOfNumber = [1,2,3]
tlistOfNumberConcat = tlistOfNumber ++ [4,5,6]
tlistOfChar = ['a',' ','l','i','s','t',' ','o','f',' ','c','h','a','r']
tlistOfCharIsAString = tlistOfChar ++ " are string, it work with all list function"
-- cons
tcons = 'a':" consed list"
tcons2 = 'a':'n':"other consed list"
tTailOfString = head tString
tHeadOfString = tail tString
tInitOfString = init tString
tfourFirst = take 4 trange
-- string
tString = "a string"
tFourthLetterOfString = tString !! 3
-- generator
trange = [1..10]
trangeByTwo = [2,4..10]
trangeInfinite = [1..]
trepeat = repeat 't'
tcycle = cycle ['/', '-', '\\', '-']
treplicate3time = replicate 3 "time"
tlistcomprehension = [ x * 5 | x <- [1..] , x < 10 ]
-- tuple
ttreple a b c = (a,b,c)
ttuple a b = (a,b)
ttupleA tpl = fst tpl
ttupleB tpl = snd tpl
tzip = zip [1..3] [3..6]
-- |how you document and type a function properly
-- |this will be added to function definition
-- this will not
tproc :: String
tproc = "A String is returned"
{-|
   multiline
   comment
   FTW
-}
tmonum :: Int -> Int
tmonum a = a
-- |return factiorial of n
tfact :: Int -> Int
tfact n = product [1..n]
-- |reuse long type name
ttoint :: (Num n) => n -> Int
ttoint n = 1
-- |pattern
tpat :: String -> Bool
tpat "Moe" = True
tpat "Homer" = True
tpat m = False
-- |guard
tgui :: String -> Bool
tgui name
  | ((take 3 name)) == "gui" = True
  | otherwise = False
-- |guard with where clause
tgui2 :: String -> Bool
tgui2 name
 | threeFirst == lower = True
 | threeFirst == startUpperCase = True
 | threeFirst == allUpperCase = True
 | otherwise = False
 where threeFirst = take 3 name
       lower = "gui"
       startUpperCase = "Gui"
       allUpperCase = "GUI"	
-- |where clause is not exclusive to guard
tinitial firstname lastname = [f] ++ ", " ++ [l] ++ "."
 where (f:_) = firstname
       (l:_) = lastname
-- |let expression are like where but is only accessible from the inner code
tinitial2 firstname lastname = 
 let f = head firstname
     l = head lastname
 in  [f] ++ ", " ++ [l] ++ "."
-- im a declaration
tten = (let first = 1 ; last = 10 in [first..last])
-- |replace guard with let expression
tgui3 name =
 let tgui3' "gui" = True
     tgui3' "Gui" = True
     tgui3' "gui" = True
     tgui3' name' = False
 in  (tgui3' (take 3 name))
-- |There is also case expression
tlstabout lst = "the list is " ++ case lst of [] -> "empty"
                                              [_] -> "singleton"
                                              as -> "gluton"
-- |quicksort
tquicksort :: (Ord a) => [a] -> [a]
tquicksort [] = []
tquicksort (pivot:rest) =
 let biggest = tquicksort [elem | elem <- rest, elem >= pivot]
     smallest = tquicksort [elem | elem <- rest, elem < pivot]
 in  biggest ++ [pivot] ++ smallest
-- |let as code place
ttriangler a b c = 
 let h = a^2 + b^2
     yes = c^2 ==h
 in  yes