Ocaml Abstract Syntax Tree - Syntax Error

Question

I am still very new to OCaml and have written a scanner, parser and Abstract Syntax Tree (with a pretty printer) for a small language. My AST used to compile fine but now it's giving me a syntax error and I can't figure out why.

Here is the part of the code where I get the error:

 1    type op = Add | Sub | Mult | Div | Equal | Neq | Less | Leq | Greater | Geq
 2        | And | Or | Not
 3        
 4        
 5   type primitive = Int | Bool | String
 6   type objtype = Room | Thing | GameMainDef
 7
 8   type program = odecl list
 9
10   type odecl = {
11   object_name : string;
12   obj_type : objtype;
13   attrib : (string * expr) list;   
14   funcdecl : f_decl list;
15   }
16  
17  type expr =
18     Literal of int
19   | BoolLiteral of bool
20   | StringLiteral of string   
21   | Id of string
22   | Unaryop of op * expr
23   | Binop of expr * op * expr
24   | Assign of string * expr
25   | Call of string * expr list
26   | Noexpr
27
28  type stmt =
29     Block of stmt list
30   | Expr of expr
31   | If of expr * stmt * stmt
32   | For of expr * expr * expr * stmt
33   | While of expr * stmt
34  
35   type fdecl = {
36     fname : string;
37     locals : (primitive * string) list;
38     body : stmt list;
39    }
40
41    let rec string_of_type t = match t with
42     Bool -> "bool"
43   | Int -> "int"
44   | String -> "string"
45   | Room -> "Room"
46   | Thing -> "Thing"
47   | MainGameDef -> "MainGameDef"

There are about 100 more lines of code (the pretty printer).

I get the following syntax error:

File "Ast.mli", line 41, characters 0-3: Error: Syntax error

If anybody has any advice, it would be very appreciated. Thank you! :)

Answer 1

According to your updated post, you are compiling an mli file. Mli is an interface file where you cannot write function/value definitions. You got the syntax error because let is not valid in an interface.