PL-SML2: Data-Type

Data-type:

• Tuple: each of types, refer to values by position
• Option: one of types
• List: three building blocks
• Records: refer to values by fields or names

Constructor and Deconstrctor:

---

• Constructor:
  E.g.
  datatype mytype = TwoInts of int*int
  | Str of String
  | Pizza

• Deconstructor:
  fun f x =
  case x of
  Pizza => 3
  | TwoInts(i1, i2) => i1 + i2
  | Str s => String.size s

Pattern Matching

---

case of

Exception

---

exception MyFirstException
exception MySecondException of int*int
raise MyFirstExcetion
raise (MySecondException(7,9))
e1 handle MyFirstException => e2
e1 handle MySecondException(7,9) => e2

Polymorphic datatypes

---

   datatype `a option = NONE | SOME `a
   datatype `a mylist = Empty | Cons of `a * `a mylist
   datatype (`a, `b) tree = 
            Node of `a*(`a, `b) tree *(`a, `b) tree
          | Leaf of `b

Syntactic Sugar:

---

Syntactic: can describe the semantics entirely by the corresponding record syntax
Sugar: make the language sweeter

Tail-recursion

---

tail-call : if the result of f x is the "immediate result" for the enclosing function body, the f x is a tail-call.
Precise definition: A tail-call is a function call in tail position.