I recently got a confusing error msg, and reduced it to a small case:
f1 :: Monad m => m Bool
f1 = f2 0 0 'a'
f2 :: Monad m => Int -> Float -> m Bool
f2 = undefined
From this, it's clear that f2 is being given an extra Char argument it
didn't ask for. However, the error msg (ghc 7.8.3) is:
This seems straightforwardly to be a bug, to me. HEAD gives the same behavior
you report below. Please post on the bug tracker at
https://ghc.haskell.org/trac/ghc/newticket
Thanks!
Richard
On Dec 4, 2014, at 1:50 PM, Evan Laforge wrote:
> I recently got a confusing error msg, and reduced it t
Int -> Float -> Char -> Bool *is* in fact a valid type for f2, since ((->)
Char) is a Monad. However, I agree the error message is confusing,
especially the "expected n, but got n" part.
-Brent
On Thu, Dec 4, 2014 at 1:50 PM, Evan Laforge wrote:
> I recently got a confusing error msg, and redu
I don't see a bug here. f2 is perfectly OK, so, let's examine f1 more closely.
It tries to get `m Bool` by applying f1 to three arguments: 0, 0, and 'a'. Now,
since `f2` has the type `Int -> Float -> n Bool`, where `n` is of kind `* -> *`
(and an instance of `Monad` class, but it's not yet the t
It seems to be an instance of
https://ghc.haskell.org/trac/ghc/ticket/7869
But it is fixed (both in HEAD and 7.8). Probably the fix is partial?
On Thu, 2014-12-04 at 14:53 -0500, Richard Eisenberg wrote:
> This seems straightforwardly to be a bug, to me. HEAD gives the same behavior
> you report
On Thu, Dec 4, 2014 at 12:59 PM, migmit wrote:
> It tries to get `m Bool` by applying f1 to three arguments: 0, 0, and 'a'.
> Now, since `f2` has the type `Int -> Float -> n Bool`, where `n` is of kind
> `* -> *` (and an instance of `Monad` class, but it's not yet the time to look
> for instanc
The reason I said "That's a bug!" so confidently is because of the "expected n
but got n" part. Even if everything else is OK, we need to fix that one bit.
And I tend to agree about using heuristics to report better error messages in
the presence of instantiating a type variable with (->). I've
But it says `expected Char -> Bool, got Char -> m Bool', note the `m' type
constructor in the second one. So it's not `n' vs. `n'.
On Dec 5, 2014 10:50 PM, "Richard Eisenberg" wrote:
> The reason I said "That's a bug!" so confidently is because of the
> "expected n but got n" part. Even if everyt
I think Richard is referring to "The function ‘f2’ is applied to three
arguments,
but its type ‘Int -> Float -> Char -> Bool’ has only three". Note
"applied to three ... but ... only three". Here n = three.
-Brent
On Fri, Dec 5, 2014 at 9:55 AM, Dr. ÉRDI Gergő wrote:
> But it says `expec
I was going to ask if I should go ahead and file a bug anyway, but I
just noticed commit 09b7943321f89b945d10f8a914f4c2cbf73dff91 seems to
fix it.
Many thanks to Yuras!
On Fri, Dec 5, 2014 at 7:50 AM, Brent Yorgey wrote:
> I think Richard is referring to "The function ‘f2’ is applied to three
>
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