Fix infinite loop with unclosed comments

Author: engboris

src/expr.ml

@@ -32,8 +32,6 @@ let focus_op = "@"
 
 let def_op = ":="
 
-let typedef_op = "::"
-
 let expect_op = "=="
 
 let params_op = "$params"

src/lexer.ml

@@ -16,7 +16,7 @@ let rec comment lexbuf =
 
 and comments lexbuf =
   match%sedlex lexbuf with
-  | "'''" -> read lexbuf
+  | "'''" | eof -> read lexbuf
   | _ ->
     ignore (Sedlexing.next lexbuf);
     comments lexbuf