cohalz

let rec mem a s =
  match (a,s) with
  | (_,[]) -> false
  | (b,x::xs) -> if b = x then true else mem b xs

cohalz

let rec max_list = function
  | [] -> 0
  | x::xs -> let max = max_list xs in if x >= max then x else max

cohalz

let rec take lst n = 
  match (lst,n) with
  | ([],_) -> []
  | (x::xs,m) -> if m <= 0 then [] else x::(take xs) (m-1)
  
let rec drop lst n = 
  match (lst,n) with
  | ([],_) -> []
  | (x::xs,m) -> if m > 1 then take xs (m-1) else xs

cohalz

let rec filter p = function
  | [] -> []
  | x::xs -> if p x then x::filter p xs else filter p xs

cohalz

(*´･_･`*)
let rec unzip = function
  | [] -> ([],[])
  | (x,y)::xs -> (x::fst (unzip xs),y::snd (unzip xs))

cohalz

let rec zip lst1 lst2 =
  match (lst1,lst2) with
  | ([],_) | (_,[]) -> []
  | ((x::xs),(y::ys)) -> (x,y)::zip xs ys

cohalz

let rec concat = function
  | [] -> []
  | []::xs -> concat xs
  | (x::ls)::xs -> x :: concat (ls::xs)

cohalz

let rec nested_length = function
  | [] -> 0
  | []::xs -> nested_length xs
  | (x::ls)::xs -> 1 + nested_length (ls::xs)

cohalz

let romanmap = [(1000,"M");(900,"CM");(500,"D");(400,"CD");(100,"C");(90,"XC");(50,"L");(40,"XL");(10,"X");(9,"IX");(5,"V");(4,"IV");(1,"I")]

let rec roman romanmap n =
  match romanmap with
  | [] -> ""
  | x::xs -> if fst x <= n then snd x ^ roman romanmap (n - fst x)  else roman xs n

cohalz

let rec downto1 = function
  | n -> if n < 1 then [] else n::downto1 (n-1)