Trees and languages

7. (t lists)
   How to model streams that can be either empty or composed with a value and another stream ?

type 't Str = End | Add of 't*('t Str);;

let s = Add (14,Add(7,Add(16,End)));;

let (<>) v s = Add (v,s);;
let s = 14 <> (7 <> (16 <> End));;

8. How to define a catenation operator on streams ?

let rec cat s1 s2 = 
  match s1 with 
  | End       -> s2
  | Add(v,s3) -> Add(v,cat s3 s2);;

cat s s;;

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