[MLton] Bug in signature ascription
Wesley W. Terpstra
terpstra at gkec.tu-darmstadt.de
Tue Feb 6 13:01:12 PST 2007
Attached are fold.sig and fold.sml. I am using a svn mlton from Jan 7th.
When compiling, you'll get the following error:
> Error: fold.sml 16.19.
> Variable type in structure disagrees with signature.
> variable: step0
> structure: _ -> ((_ * [??? -> ???]) -> (((_ * [??? -> ???]) ->
> _) -> _))
> signature: _ -> ((_ * ['a]) -> (((_ * ['a]) -> _) -> _))
> Error: fold.sml 16.19.
> Variable type in structure disagrees with signature.
> variable: step1
> structure: _
> -> ((_ * [??? -> ???]) -> (_ -> (((_ * [??? -> ???])
> -> _) -> _)))
> signature: _ -> ((_ * ['a]) -> (_ -> (((_ * ['a]) -> _) -> _)))
> compilation aborted: parseAndElaborate reported errors
However, when the signature ascription from EITHER Fold or Foldr is
removed, it compiles.
The error only appears when the signature is bound to both structures
at the same time.
Even if the error is correct, I should have gotten it with just
binding Foldr.
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