[MLton-devel] cvs commit: new front end

[Matthew Fluet]

>   3. Confusing type error messages.
>   4. Improvements to type error messages.

I know they are at the bottom of the list, but I find the use of "_"
(dontCare) in error messages a little confusing, especially when fixing
the immediate type error can simply require fixing another one down the
line:

[fluet@nonnel temp]$ cat z.sml
datatype t = T of int -> int

val x = T ()
val x = T ord


datatype 'a u = U of 'a -> 'a

val x = U ()
val x = U ord
[fluet@nonnel temp]$ mlton -stop tc z.sml
Error: z.sml 3.9: function applied to incorrect argument
   expects: _ -> _
   but got: unit
   in: T ()
Error: z.sml 4.9: function applied to incorrect argument
   expects: int -> _
   but got: char -> _
   in: T ord
Error: z.sml 9.9: function applied to incorrect argument
   expects: _ -> _
   but got: unit
   in: U ()
Error: z.sml 10.9: function applied to incorrect argument
   expects: _ -> char
   but got: _ -> int
   in: U ord
compilation aborted: elaborate reported errors


It's especially the fact that the expects in the first two messages is
definitely known to be  int -> int; likewise, with ord, the got is
definitely  char -> int.  The last message is especially confusing, since
having expected  _ -> char means that 'a has been pinned as a char.



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