[MLton] cvs commit: different layout for type error messages

[Stephen Weeks]

sweeks      04/05/25 20:20:52

  Modified:    mlton/control control.sml
  Log:
  MAIL different layout for type error messages
  
  I was thinking that type error messages would be easier to read if we
  didn't put the file position and error description all on the same
  line.  Instead, put the error description on its own line just after
  the file position.  So, instead of
  
  Error: z.sml 1.9: function not of arrow type
     function: [int]
     in: 1 2
  
  We would get
  
  Error: z.sml 1.9.
     Function not of arrow type.
     function: [int]
     in: 1 2
  
  This isn't a great example since z.sml is such a small file name.
  But, this approach has three visual advantages as I see it.  First,
  the error description is always in the same place, instead of having
  its start being dependent on the length of the file position.  Second,
  the error description will be much less likely to go past 80 columns,
  since it starts in column 3.  Third, since one usually uses automated
  tools to put the cursor at the appropriate file position, one doesn't
  even usually look at the file position anyways -- this makes it easier
  to jump to what you want to read.
  
  Anyways, this checkin implements the change.  Let me know what you
  think.
  
  Actually, with the extra space, I was thinking of writing out the
  information on the file position, just to make it easier for beginners
  (who might not use an automated tool), since I don't think it matters
  for the rest of us.  Something like
  
  Error in z.sml on line 1 column 9.
     Function not of arrow type.
     function: [int]
     in: 1 2
  
  But I haven't checked that in yet.
  
  Another format that I considered was the following, which redundandtly
  displays "error", but is perhaps more uniform.
  
  Error in z.sml on line 1 column 9.
     error: function not of arrow type
     function: [int]
     in: 1 2

Revision  Changes    Path
1.118     +8 -3      mlton/mlton/control/control.sml

Index: control.sml
===================================================================
RCS file: /cvsroot/mlton/mlton/mlton/control/control.sml,v
retrieving revision 1.117
retrieving revision 1.118
diff -u -r1.117 -r1.118
--- control.sml	19 May 2004 12:55:57 -0000	1.117
+++ control.sml	26 May 2004 03:20:51 -0000	1.118
@@ -745,10 +745,15 @@
 	    case Region.left r of
 	       NONE => "<bogus>"
 	     | SOME p => SourcePos.toString p
+	 val msg = Layout.toString msg
+	 val msg =
+	    Layout.str
+	    (concat [String.fromChar (Char.toUpper (String.sub (msg, 0))),
+		     String.dropPrefix (msg, 1),
+		     "."])
 	 in
-	    outputl (align [seq [str (concat [kind, ": "]),
-				 str p, str ": ", msg],
-			    indent (extra, 3)],
+	    outputl (align [seq [str (concat [kind, ": "]), str p, str "."],
+			    indent (align [msg, extra], 3)],
 		     Out.error)
       end
 in