Lst.map;;
"hello world";;
"hello" ^ "world";;
let h = "hello";;
h.[0];;
type t = char list;;
['a';'b';'c'];;
[1;2;3];;
let rec sum n = if n <= 0 then 0 else n + sum (n-1);;
sum 3;;
#trace sum;;
sum 3;;
#trace Lst.replicate;;
Lst.replicate 3 'c';;
let toplevel_printer fmt s = 
 Format.fprintf fmt "\"%s\"" (String.escaped(to_string s)) 
;;
open Strng;;
let toplevel_printer fmt s = 
 Format.fprintf fmt "\"%s\"" (String.escaped(to_string s)) ;;
['a';'c'];;
#uninstall Strng.toplevel_printer;;
#uninstall_printer Strng.toplevel_printer;;
#remove_printer Strng.toplevel_printer;;
['a';'c'];;
#install_printer Strng.toplevel_printer;;
['a';'c'];;
let p = (7,3,"*******";" hello ";"*******");;
let p = (7,3,["*******";" hello ";"*******"]);;
Picture.p;;
p;;
#remove_printer Picture.toplevel_printer;;
p;;
#remove_printer Strng.toplevel_printer;;
p;;
#install_printer Strng.toplevel_printer;;
#install_printer Picture.toplevel_printer;;
p;;
let p1 = (5,1,of_string "hello");;
open Strng;;
let p1 = (5,1,of_string "hello");;
let p2 = (5,1,of_string "world");;
Picture.above p1 p2;;
let p2 = (5,1,[of_string "world"]);;
let p1 = (5,1,[of_string "hello"]);;
Picture.above p1 p2;;
Lst.foldr;;
Lst.foldr (+) 0 [1;2;3];;
Lst.foldr (Picture.above) 0 ps;;
let stack ps = Lst.foldr1 (Picture.above) ps;;
stack [p1;p1;p2;p2];;
(* useless foldr1 function since base case is missing *)
let rec foldr1 f = function
 | [] -> failwith "foldr1.empty"
 | x::xs -> f x (foldr1 f xs);;
foldr1 (+) [];;
foldr1 (+) [1;2;3];;
let rec foldr1 f = function
 | [] -> failwith "foldr1.empty"
 | [x] -> x
 | x::xs -> f x (foldr1 f xs);;
let rec zip_with f xs ys = match (xs,ys) with
  | ([],_)
  | (_,[]) -> []
  | (x::xs,y::ys) -> f x y::zip_with f xs ys;;
zip_with ( * ) [1;2] [3;4;5];;
zip_with ( * ) [] [];;
let h = pixel 'h';;
open Picture;;
let h = pixel 'h';;
let e = pixel 'e';;
beside h e;;
let row s = spread(Lst.map pixel s);;
row ['h';'e';'l';'l';'o'];;
row [1;2;3];;
empty 3 3;;
#remove_printer Picture.toplevel_printer;;
empty 3 3;;
#install_printer Picture.toplevel_printer;;
empty 3 3;;
open Picture;;
tile [[p00;p01;p02];[p10;p11;p12]];;
tile_with 1 1 [[p00;p01;p02];[p10;p11;p12]];;
let rec join d = function
 | [] -> []
 | x::xs -> x@d@join d xs;;
let test = tile_with 1 1 [[p00;p01;p02];[p10;p11;p12]];;
to_strng test;;
#remove_printer Strng.toplevel_printer;;
to_strng test;;
empty 0 3;;
empty 1 0;;
let empty w h = 
 if w = 0 then (0,h,Lst.replicate h []) 
 else if h = 0 then (w,0,[]) 
 else empty w h 
(* rotate : t -> t *)
let rotate (w,_,pss) = 
 Lst.foldr (fun l p -> beside p (column l)) (empty 0 w) pss 
;;
test;;
rotate test;;