es2.fsx

#r @"dict.dll"


open dict

// ii

let env1 = insert "x" 1 empty
let env2 = insert "y" 2 env1
let env3 = insert "a" 10 env2
let env4 = insert "h" 5 env3
let env5 = insert "d" 7 env4

lookup "x" env5
lookup "d" env5
toList env5

// iii

type aexp =
  | C of int
  | V of string
  | Sum of aexp * aexp
  | Def of string * aexp * aexp

let e1 = Def( "z" , Sum(V "x", C 10), Sum(V "y", V "z") )
let e2 = Def( "x" , C 100 ,  Sum(V "x", V "y") )

let rec aeval t env =
    match t with
    | C n ->  n
    | V s ->  lookup s env
    | Sum(t1,t2)   -> aeval t1 env + aeval t2 env
    | Def(x,e1,e2) -> aeval e2 (insert x (aeval e1 env) env)

aeval e1 env5
aeval e2 env5