Runtime error as a special exception

lib/Base/Assert.fram

@@ -14,7 +14,7 @@ pub let runtimeError {type T} =
   (extern dbl_runtimeError : String ->[] T)
 
 (** Explicitly assert, that this case is impossible *)
-pub let assertImpossible {?msg : String} () =
+pub let impossible {?msg : String} () =
   runtimeError
     match msg with
     | None     => "Assertion failed"
@@ -25,4 +25,4 @@ pub let assertImpossible {?msg : String} () =
 pub let assert {?msg} b =
   if b then ()
   else
-    assertImpossible {?msg} ()
+    impossible {?msg} ()

src/Eval/Eval.ml

@@ -4,6 +4,8 @@
 
 open Value
 
+exception Runtime_error = External.Runtime_error
+
 (** Evaluator *)
 (* ========================================================================= *)
 
@@ -90,7 +92,7 @@ let rec eval_expr env (e : Lang.Untyped.expr) cont =
     end
   | ERepl func -> eval_repl env func cont
   | EReplExpr(e1, tp, e2) ->
-    Printf.printf ": %s\n" tp;
+    Printf.printf ": %s\n%!" tp;
     eval_expr env e1 (fun v1 ->
       Printf.printf "= %s\n" (to_string v1);
       eval_expr env e2 cont)

src/Eval/Eval.mli

@@ -4,4 +4,6 @@
 
 (** Evaluator *)
 
+exception Runtime_error
+
 val eval_program : Lang.Untyped.program -> unit

src/Eval/External.ml

@@ -4,26 +4,32 @@
 
 open Value
 
+exception Runtime_error
+
 (** External functions *)
 (* ========================================================================= *)
 
+let runtime_error msg =
+  Printf.eprintf "Runtime error: %s\n%!" msg;
+  raise Runtime_error
+
 let unit_fun f = VFn (fun v cont -> cont (f ()))
 
 let int_fun f = VFn (fun v cont ->
   match v with
   | VNum n -> cont (f n)
-  | _ -> failwith "Runtime error!")
+  | _ -> runtime_error "Not an integer")
 
 let str_fun f = VFn (fun v cont ->
   match v with
   | VStr s -> cont (f s)
-  | _ -> failwith "Runtime error!")
+  | _ -> runtime_error "Not a string")
 
 let list_chr_fun f = VFn (fun v cont ->
   let rec parse_list = function
   | VCtor(0, []) -> []
   | VCtor(1, [VNum x; xs]) -> Char.chr x :: parse_list xs 
-  | _ -> failwith "Runtime error!" in
+  | _ -> runtime_error "Not a list" in
   cont (f @@ parse_list v))
 
 let v_unit = VCtor(0, [])
@@ -44,7 +50,7 @@ let int_cmpop op = int_fun2 (fun x y -> of_bool (op x y))
 let int64_fun f = VFn (fun v cont ->
   match v with
   | VNum64 n -> cont (f n)
-  | _ -> failwith "Runtime error!")
+  | _ -> failwith "Not a 64-bit integer")
 
 let int64_fun2 f = int64_fun (fun x -> int64_fun (f x))
 
@@ -55,9 +61,6 @@ let int64_cmpop op = int64_fun2 (fun x y -> of_bool (op x y))
 
 let str_cmpop op = str_fun (fun s1 -> str_fun (fun s2 -> of_bool (op s1 s2)))
 
-let runtime_error msg =
-  failwith ("Runtime error: " ^ msg)
-
 let extern_map =
   [ "dbl_runtimeError", str_fun runtime_error;
     "dbl_negInt",      int_unop ( ~- );

src/dbl.ml

@@ -79,3 +79,4 @@ let _ =
     | Some fname -> Pipeline.run_file fname
   with
   | InterpLib.Error.Fatal_error -> exit 1
+  | Eval.Runtime_error -> exit 2