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+## 2023 Fall
+
+- [COSE 212: Programming Languages]({{< relref "cose212/2023/_index.md" >}})
+- AAA 616: Program Analysis
+
 ## 2023 Spring
 
 - [COSE 312: Compilers](https://github.com/kupl-courses/COSE312-2023spring)
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++++
+draft = false
+title = 'COSE212-23F'
++++
+
+# Programming Languages, 2023 Fall
+
+## Course Information
+
+- Instructor: [Hakjoo Oh]({{< ref "/members/hakjoo-oh" >}})
+- TAs: [Minsu Kim]({{< "/members/minsu-kim" >}}), Doyeon Hwang
+- Lecture: 09:00-11:45 on Mondays and Wednesday (8 weeks)
+- [Syllabus](./syllabus.pdf)
+
+## References
+
+- [프로그래밍 언어의 원리](./pl-book.pdf)
+- [Essentials of Programming Languages](https://www.amazon.com/gp/product/0262062798?ie=UTF8&tag=ucmbread-20&linkCode=as2&camp=1789&creative=9325&creativeASIN=0262062798)
+- [Notes on Programming Languages (in Korean)](./pl-book-draft.pdf)
+
+## Slides
+
+- Course Overview: [lec0.pdf](./slides/lec0.pdf)
+- (Part 1) Preliminaries
+    - Inductive Definitions: [lec1.pdf](./slides/lec1.pdf), [lec2.pdf](./slides/lec2.pdf)
+    - Functional Programming: [lec3.pdf](./slides/lec3.pdf), [lec4.pdf](./slides/lec4.pdf)
+- (Part 2) Basic Concepts
+    - Expressions: [lec5.pdf](./slides/lec5.pdf), [code](./slides/let.ml)
+    - Procedures: [lec6.pdf](./slides/lec6.pdf)
+    - Lexical scoping: [lec7.pdf](./slides/lec7.pdf)
+    - States: [lec8.pdf](./slides/lec8.pdf)
+    - Records, Pointers, and garbage collection: [lec9.pdf](./slides/lec9.pdf)
+- (Part 3) Advanced Concepts
+    - Static Type System: [lec10.pdf](./slides/lec10.pdf), [lec11.pdf](./slides/lec11.pdf), [lec12.pdf](./slides/lec12.pdf)
+    - Automatic Type Inference: [lec13.pdf](./slides/lec13.pdf), [lec14.pdf](./slides/lec14.pdf), [lec15.pdf](./slides/lec15.pdf)
+    - Polymorphic Type System: [lec16.pdf](./slides/lec16.pdf)
+    - Lambda Calculus: [lec17.pdf](./slides/lec17.pdf)
+    - Operational and denotational semantics: [lec18.pdf](./slides/lec18.pdf)
+- Course Review: [lec19.pdf](./slides/lec19.pdf)
+
+## Programming Assignment
+
+- Programming exercises: [ocaml-exercises.pdf](./hw/ocaml-exercises.pdf)
+- Final Project (interpreter and type checker): [project.pdf](./hw/project.pdf) [template](./hw/ml_minus.ml)
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+(* Do not open any module *)
+
+(***********************)
+(*  Library functions  *)
+(***********************)
+
+let rec fold_left : ('a -> 'b -> 'a) -> 'a -> 'b list -> 'a
+= fun f accu lst ->
+  match lst with
+  | [] -> accu
+  | hd::tl -> fold_left f (f accu hd) tl
+
+let rec map : ('a -> 'b) -> 'a list -> 'b list
+= fun f lst ->
+  match lst with
+  | [] -> []
+  | hd::tl -> (f hd)::(map f tl)
+
+(***********************)
+(******  Syntax  *******)
+(***********************)
+
+type program = exp
+and exp = 
+  | UNIT
+  | TRUE
+  | FALSE
+  | CONST of int
+  | VAR of var
+  | ADD of exp * exp
+  | SUB of exp * exp
+  | MUL of exp * exp
+  | DIV of exp * exp
+  | EQUAL of exp * exp
+  | LESS of exp * exp
+  | NOT of exp
+  | NIL
+  | CONS of exp * exp      
+  | APPEND of exp * exp
+  | HEAD of exp
+  | TAIL of exp
+  | ISNIL of exp
+  | IF of exp * exp * exp
+  | LET of var * exp * exp
+  | LETREC of var * var * exp * exp
+  | LETMREC of (var * var * exp) * (var * var * exp) * exp
+  | PROC of var * exp
+  | CALL of exp * exp
+  | PRINT of exp
+  | SEQ of exp * exp
+and var = string
+
+(***********************)
+(**  Example programs **)
+(***********************)
+
+(*
+  let f = proc (x) (x - 11)
+  in (f (f 77))
+*)
+let proc1 = 
+  LET ("f", PROC ("x", SUB (VAR "x", CONST 11)),
+    CALL (VAR "f", CALL (VAR "f", CONST 77)))
+
+(*
+  ((proc (f) (f (f 77))) (proc (x) (x-11)))
+*)
+let proc2 = 
+  CALL (PROC ("f", CALL (VAR "f", CALL (VAR "f", CONST 77))), 
+        PROC ("x", SUB (VAR "x", CONST 11)))
+
+(*
+  let x = 1
+  in let f = proc (y) (x + y)
+     in let x = 2
+        in let g = proc (y) (x + y)
+        in  (f 1) + (g 1)
+*)
+let let1 = 
+  LET ("x", CONST 1, 
+    LET ("f", PROC ("y", ADD (VAR "x", VAR "y")),
+      LET ("x", CONST 2, 
+         LET ("g", PROC ("y", ADD (VAR "x", VAR "y")), 
+            (ADD (CALL (VAR "f", CONST 1), 
+                  CALL (VAR "g", CONST 1)))))))
+
+(*
+  letrec even(x) = if (x = 0) then true else odd(x-1)
+         odd(x) = if (x = 0) then false else even(x-1)
+  in (even 13)
+*)
+let evenodd = 
+  LETMREC (("even", "x", IF (EQUAL (VAR "x", CONST 0), TRUE, CALL (VAR "odd",  SUB (VAR "x", CONST 1)))),
+           ("odd" , "x", IF (EQUAL (VAR "x", CONST 0), FALSE, CALL (VAR "even", SUB (VAR "x", CONST 1)))),
+  CALL (VAR "odd", CONST 13))
+
+
+(*
+  letrec double(x) = if (x = 0) then 0 else (double (x-1) + 2
+  in (double 6)
+*)
+let double = 
+  LETREC ("double", "x", IF (EQUAL (VAR "x", CONST 0), 
+                            CONST 0, 
+                            ADD (CALL (VAR "double", SUB (VAR "x", CONST 1)) , 
+                                 CONST 2)), 
+    CALL (VAR "double", CONST 6))
+
+(*
+letrec factorial(x) = 
+         if (x = 0) then 1 
+         else factorial(x-1) * x
+in letrec loop n = 
+     if (n = 0) then ()
+     else (print (factorial n); loop (n-1))
+   in (loop 10)
+*)
+let fact = 
+LETREC ("factorial", "x", 
+          IF (EQUAL (VAR "x", CONST 0), CONST 1, 
+              MUL (CALL (VAR "factorial", SUB (VAR "x", CONST 1)), VAR "x")), 
+  LETREC ("loop", "n", 
+    IF (EQUAL (VAR "n", CONST 0), UNIT, 
+        SEQ (PRINT (CALL (VAR "factorial", VAR "n")), 
+             CALL (VAR "loop", SUB(VAR "n", CONST 1)))), 
+      CALL (VAR "loop", CONST 10)))
+           
+(*
+in letrec range(n) = 
+      if (n = 1) then (cons 1 nil)
+      else n::(range (n-1))
+in (range 10)
+*)
+let range = 
+LETREC ("range", "n", 
+            IF (EQUAL (VAR "n", CONST 1), CONS (CONST 1, NIL),
+                CONS (VAR "n", CALL (VAR "range", SUB (VAR "n", CONST 1)))), 
+     CALL (VAR "range", CONST 10))
+
+(*
+letrec reverse(l) = 
+  if (isnil l) then []
+  else (reverse (tl l)) @ (cons hd l)
+in (reverse (cons (1, cons (2, cons (3, nil)))))
+*)
+let reverse = 
+LETREC ("reverse", "l", 
+          IF (ISNIL (VAR "l"), NIL, 
+              APPEND (CALL (VAR "reverse", TAIL (VAR "l")), 
+                      CONS (HEAD (VAR "l"), NIL))), 
+     CALL (VAR "reverse", 
+           CONS (CONST 1, CONS (CONST 2, CONS (CONST 3, NIL)))))
+
+let reverse2 = 
+LETREC ("reverse", "l", 
+          IF (ISNIL (VAR "l"), NIL, 
+              APPEND (CALL (VAR "reverse", TAIL (VAR "l")), 
+                      CONS (HEAD (VAR "l"), NIL))), 
+     CALL (VAR "reverse", 
+           CONS (CONS (CONST 1, NIL), CONS (CONS (CONST 2, NIL), CONS (CONS (CONST 3, NIL), NIL)))))
+
+
+let zfact = 
+  LET ("fix", 
+    PROC ("f", 
+      CALL (PROC ("x", CALL (VAR "f", PROC ("y", CALL (CALL (VAR "x", VAR "x"), VAR "y")))), 
+            PROC ("x", CALL (VAR "f", PROC ("y", CALL (CALL (VAR "x", VAR "x"), VAR "y")))))),
+    LET ("f", CALL (VAR "fix", 
+            PROC ("f", PROC ("x", 
+          IF (EQUAL (VAR "x", CONST 0), CONST 1, 
+              MUL (CALL (VAR "f", SUB (VAR "x", CONST 1)), VAR "x"))))), 
+           CALL (VAR "f", CONST 10)))
+
+let zrange = 
+  LET ("fix", 
+    PROC ("f", 
+      CALL (PROC ("x", CALL (VAR "f", PROC ("y", CALL (CALL (VAR "x", VAR "x"), VAR "y")))), 
+            PROC ("x", CALL (VAR "f", PROC ("y", CALL (CALL (VAR "x", VAR "x"), VAR "y")))))),
+
+
+    LET ("f", CALL (VAR "fix", 
+            PROC ("range", PROC ("n", 
+               IF (EQUAL (VAR "n", CONST 1), CONS (CONST 1, NIL),
+                 CONS (VAR "n", CALL (VAR "range", SUB (VAR "n", CONST 1))))))), 
+           CALL (VAR "f", CONST 10)))
+
+let poly = 
+    LET ("f", PROC("x", VAR "x"), 
+      IF(CALL (VAR "f", TRUE), CALL (VAR "f", CONST 1), CALL (VAR "f", CONST 2)))
+
+let lst =
+    CONS (CONST 1, CONS (CONST 2, CONS (TRUE, NIL)))
+
+(***********************)
+(*****  Problem 1  *****)
+(***********************)
+
+type value = 
+  | Unit 
+  | Int of int 
+  | Bool of bool 
+  | List of value list
+  | Procedure of var * exp * env 
+  | RecProcedure of var * var * exp * env
+  | MRecProcedure of var * var * exp *
+                     var * var * exp * env
+and env = (var * value) list
+
+exception UndefinedSemantics
+
+let rec string_of_value v = 
+  match v with
+  | Int n -> string_of_int n
+  | Bool b -> string_of_bool b
+  | List lst -> "[" ^ fold_left (fun s x -> s ^ ", " ^ x) "" (map string_of_value lst) ^ "]"
+  | _ -> "(functional value)"
+
+let empty_env = []
+let extend_env (x,v) e = (x,v)::e
+let rec lookup_env x e = 
+  match e with
+  | [] -> raise (Failure ("variable " ^ x ^ " is not bound in env")) 
+  | (y,v)::tl -> if x = y then v else lookup_env x tl
+
+let rec eval : exp -> env -> value
+=fun exp env ->
+  match exp with
+  | PRINT e -> (print_endline (string_of_value (eval e env)); Unit)
+  | _ -> raise (Failure "Not implemented") (* TODO *)
+
+let runml : program -> value
+=fun pgm -> eval pgm empty_env
+
+
+(***********************)
+(*****  Problem 2  *****)
+(***********************)
+
+type typ = 
+    TyUnit 
+  | TyInt 
+  | TyBool 
+  | TyFun of typ * typ 
+  | TyList of typ
+  | TyVar of tyvar
+and tyvar = string
+
+exception TypeError
+
+(* You can invoke "fresh_tyvar()" to generate a fresh type variable *)
+let tyvar_num = ref 0
+let fresh_tyvar () = (tyvar_num := !tyvar_num + 1; (TyVar ("t" ^ string_of_int !tyvar_num)))
+
+let typecheck : program -> typ 
+=fun exp -> raise TypeError (* TODO *)
\ No newline at end of file
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+(*
+1. store this file as a file (e.g. "let.ml")
+2. type "ocaml let.ml" in the shell command line
+*)
+
+type pgm = exp 
+and exp = 
+  | CONST of int 
+  | VAR of string 
+  | ADD of exp * exp 
+  | SUB of exp * exp
+  | ISZERO of exp
+  | IF of exp * exp * exp
+  | LET of string * exp * exp
+  | READ 
+
+(*
+let x = 1 in
+  let y = let x = 2 
+          in x + x
+  in x + y
+*)
+let pgm1 = 
+  LET ("x", CONST 1, 
+    LET ("y", LET ("x", CONST 2, 
+                ADD (VAR "x", VAR "x")), 
+      (ADD (VAR "x", VAR "y"))))
+
+type value = Int of int | Bool of bool
+
+module Env = struct
+  type t = (string * value) list 
+  let empty = []
+  let rec lookup x e = 
+    match e with  
+    | [] -> raise (Failure ("Env: Not found: " ^ x))
+    | (y,v)::tl -> 
+        if y = x then v else lookup x tl 
+  let update x v e = (x,v)::e
+end 
+
+let rec eval : Env.t -> exp -> value
+=fun env exp ->
+  match exp with
+  | CONST n -> Int n
+  | VAR x -> Env.lookup x env
+  | ADD (e1, e2) -> binop env e1 e2 (+)
+  | SUB (e1, e2) -> binop env e1 e2 (-)
+  | READ -> Int (read_int ())
+  | ISZERO e -> 
+      (match eval env e with
+      | Int 0 -> Bool true
+      | Int _ -> Bool false
+      | _ -> raise (Failure "type error"))
+  | IF (e1,e2,e3) ->
+      (match eval env e1 with 
+      | Bool true -> eval env e2
+      | Bool false -> eval env e3
+      | _ -> raise (Failure "type error"))
+  | LET (x,e1,e2) ->
+      let v1 = eval env e1 in
+      let v = eval (Env.update x v1 env) e2 in
+  v
+ 
+and binop env e1 e2 op = 
+  let v1 = eval env e1 in
+  let v2 = eval env e2 in
+    match v1, v2 with 
+    | Int n1, Int n2 -> Int (op n1 n2)
+    | _ -> raise (Failure ("type error")) 
+
+let print_value v = 
+  print_endline (match v with
+  | Int n  -> string_of_int n
+  | Bool b -> string_of_bool b)
+
+let _ = print_value (eval Env.empty pgm1)
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