From: Adam Chlipala <adamc@hcoop.net>
Date: Mon, 25 Feb 2008 00:32:30 +0000 (+0000)
Subject: Improve one kind of error message
X-Git-Tag: release_2010-11-19~43
X-Git-Url: https://git.hcoop.net/hcoop/domtool2.git/commitdiff_plain/b44d16e043c802069df09c5736c2480435e56b9c

Improve one kind of error message
---

diff --git a/src/describe.sml b/src/describe.sml
index 11194af..e5850e2 100644
--- a/src/describe.sml
+++ b/src/describe.sml
@@ -112,9 +112,9 @@ fun will_be_action (t, _) =
 
 fun get_first_arg (t, _) =
     case t of
-	TArrow (t', _) => t'
+	TArrow (t', _) => SOME t'
       | TUnif (_, ref (SOME t')) => get_first_arg t'
-      | _ => raise Fail "get_first_arg failed!"
+      | _ => NONE
 
 fun hint te =
     case te of
@@ -137,9 +137,12 @@ fun describe_type_error' loc te =
 	 Option.app (describe_unification_error t1) ueo)
       |	WrongForm (place, form, e, t, ueo) =>
 	if form = "action" andalso will_be_action t then
-	    (ErrorMsg.error (SOME loc) ("Not enough arguments passed to configuration function. (" ^ place ^ ")");
-	     preface (" Expression so far:", p_exp e);
-	     preface ("Next argument type:", p_typ (get_first_arg t)))
+	    (case get_first_arg t of
+		 NONE => ErrorMsg.error (SOME loc) "You probably forgot a 'with' clause here."
+	       | SOME t' =>
+		 (ErrorMsg.error (SOME loc) ("Not enough arguments passed to configuration function. (" ^ place ^ ")");
+		  preface (" Expression so far:", p_exp e);
+		  preface ("Next argument type:", p_typ t')))
 	else
 	    (ErrorMsg.error (SOME loc) (place ^ " has a non-" ^ form ^ " type.");
 	     preface ("Expression:", p_exp e);