funclang series5: Added expr2string function for ass12.

funclang-taddeus/series5/ass12.ml

+type monop = Neg | Not
+type binop = Add | Sub | Mul | Div | Mod    (* arithmetic operators *)
+           | Eq | Ne | Lt | Le | Gt | Ge    (* relational operators *)
+           | And | Or                       (* logic operators *)
+type expr = Num of int                      (* integer constant *)
+          | Bool of bool                    (* boolean constant *)
+          | Var of string                   (* variable *)
+          | MonopAp of monop * expr         (* unary operator application *)
+          | BinopAp of binop * expr * expr  (* binary operator application *)
+          | Cond of expr * expr * expr      (* conditional expression *)
+          | Fun of string * expr            (* function abstraction *)
+          | FunAp of expr * expr            (* function application *)
+          | Let of string * expr * expr     (* variable binding *)
+          | LetRec of string * expr * expr  (* recursive variable binding *)
+
+let rec expr2string =
+    let monop2string = function
+          Neg -> "-"
+        | Not -> "not "
+    in
+    let binop2string = function
+          Add -> "+"
+        | Sub -> "-"
+        | Mul -> "*"
+        | Div -> "/"
+        | Mod -> "mod"
+        | Eq -> "="
+        | Ne -> "!="
+        | Lt -> "<"
+        | Le -> "<="
+        | Gt -> ">"
+        | Ge -> ">="
+        | And -> "&&"
+        | Or -> "||"
+    in
+    function
+      Num i -> string_of_int i
+    | Bool b -> string_of_bool b
+    | Var v -> v
+    | MonopAp (op, e) -> monop2string(op) ^ expr2string(e)
+    | BinopAp (op, e1, e2) -> expr2string(e1) ^ " " ^ binop2string(op)
+                              ^ " " ^ expr2string(e2)
+    | Cond (cond, e1, e2) -> "if " ^ expr2string(cond)
+                             ^ " then " ^ expr2string(e1)
+                             ^ " else " ^ expr2string(e2)
+    | Fun (arg, e) -> "fun " ^ arg ^ " -> " ^ expr2string(e)
+    | FunAp (e1, e2) -> "(" ^ expr2string(e1) ^ " " ^ expr2string(e2) ^ ")"
+    | Let (var, e1, e2) -> "let " ^ var ^ " = " ^ expr2string(e1)
+                           ^ " in " ^ expr2string(e2)
+    | LetRec (var, e1, e2) -> "let rec " ^ var ^ " = " ^ expr2string(e1)
+                              ^ " in " ^ expr2string(e2)
+;;
+
+(* let a = 1 in b *)
+print_endline (expr2string (Let ("a", (Num 1), (Var "b"))));;
+
+(* a + 3 *)
+print_endline (expr2string (BinopAp (Add, Var "a", Num 3)));;
+
+(* -a *)
+print_endline (expr2string (MonopAp (Neg, Var "a")));;