Functional Programming Language OCaml Tutorial

1. Functional Programming LanguageOCaml Tutorial 科大-耶鲁联合研究中心 http://kdyhcs.ustcsz.edu.cn

2. Outline Introduction Get Started OCaml Basis Basic Concepts Examples Discussion

3. Introduction • Functional programming(FP) emphasizes application of functions and has its roots in lambda calculus • The difference between function in FP and imperative languages is side effects • FP can also be accomplished in imperative languages.

4. History • 1950s LISP • 1960s APL -> J -> K • 1970s ML -> Objective Caml , Standard ML • 1980s Dependent Types -> Coq, Agda, Epigram • 1987 Haskell

5. Get Started • Install • http://caml.inria.fr/pub/distrib/ocaml-3.11/ocaml-3.11.0-win-msvc.exe • Interactive • Run “ocaml” • Objective Caml version 3.11.2 • # 1+2;; • - : int =3 • Use any text editor • Emacs/Vim • Notepad++ …

6. Get Started • Run Emacs • Visist New File -> “test.ml” • Short Keys • C-c C-s “start ocaml” • C-c C-b “eval whole file” • C-c C-r “eval selected code” • Tab “Ident” • Demo

7. OCaml • Declaring Variables • Variables in OCaml are immutable! • Declaring Functions • OCaml functions don’t have explicit “return”. The return value is the last statement.

8. OCaml • All functions and values in OCaml have a datatype • let add x y = (x + y);; • OCaml will report • val add : int -> int -> int = <fun> • which means • function “add” takes two “int” inputs and return a “int” • Generic Function • let fst x y = x • - val fst : 'a -> 'b -> 'a = <fun> • # fst 1 2 ;; • # fst "a" "b";; • # fst "a" 1;;

9. Recursion and Nested Function

10. Pattern Match • Example • Patterns can be chained together

11. High-order Functions • A high-order function is a functions that takes another function as a parameter or a function returns another function or both. • Function can be partial applied • add : int -> int -> int • add 1 : int -> int • add 1 2 : int • let f = add 1 • let result = f 2

12. High-order Functions • Composition • let double x = x * 2 • let power x = x * x • let compose f g x = g (f x) • let result = (compose double power) 4 • Pipeline • let pipe x f = f x • let result = (pipe (pipe 4 double) power)

13. Anonymous Function • Example • fun x -> x * 2 • We can rewrite examples from Page 11 • compose (fun x->x*2) (fun x->x*x) 4 • Much use of anonymous functions

14. Data Structures • Option Type • Tuples • List

15. Examples • Fibonacci number • List filter, map, fold

16. Lab • Write a calculator • Provided parser combinators • built-in parsers • integer, alpha, ident, char, string • combinators • many, sepBy, paren, chainl • infix • >> >>= <|> <?> • #use “parsec.ml”;;

17. Lab • Grammar • Exp :: Term [+-] Term • Term :: Factor [*/] Factor • Factor :: int | ( Exp ) • Get Start • let add = (char ‘+’) >> (return (+)) <?> “+” • Receive a char ‘+’ and return function (+) with possible error message “+” • let factor = (paren exp) <|> (integer <?> “integer”) • either a parened “exp” or an integer • let term = chainl factor (mul <|> div) • a list of factor chained with “mul” or “div” • let expr = chainl term (add <|> sub)

18. Lab • Write a parser for first-order logic formula • Formula :: Clause \/ Clause • Clause :: Term /\ Term • Term :: Literal | Literal Comp Literal • Literal :: id | int | bool • Eval the formula with given environment • (x:true;y:false;….)

19. TODO • Spec# • ESC/Java • Compcert • CComp