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 qdun...@gmail.com wrote:
I recently got a confusing error msg,
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 qdun...@gmail.com wrote:
I recently got a confusing error
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
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 mig...@gmail.com 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
Hi, Richard
Can you give some ideas or where to read how to properly use signletons
and unary naturals in order to be able to express such constraints?
Thanks
--
Alexander
On 30 November 2014 at 23:26, Richard Eisenberg e...@cis.upenn.edu wrote:
Hi Alexander,
Nice idea to test against the
