Would someone feel able to open a Trac ticket summarising this thread (as
well as pointing to it), and making a proposal?
Done: https://ghc.haskell.org/trac/ghc/ticket/10733
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Like this?
Either use a type annotation to specify what 't0' should be
based on these potential instance(s):
instance Foo Bar -- Defined in 'Foo.Bar'
... and possibly more from other modules that
the compiler has not yet encountered
or define the required
On 2015-08-02 at 23:17, Reid Barton rwbar...@gmail.com wrote:
It may be worth noting that the existing error message is actually
technically
correct, in the sense that what would be needed for the program to compile
is exactly an instance of the form instance Foldable t where Then the
Hello,
what Reid says is exactly right---the issue is not really about what
instances are present, the problem is that GHC can't determine how to
instantiate `t0`.
Perhaps a more direct way to describe this is as follows:
Failed to infer type `t0`
while solving constraint `Data.String.IsString
On Mon, Aug 3, 2015 at 12:43 AM, Phil Ruffwind r...@rufflewind.com wrote:
I think the error message could be made clearer simply by emphasizing the
fact
that type ambiguity over the lack of instances.
Ambiguous type variable 't0' arising from a use of
elem :: a - t0 a - Bool
On 2015-08-03 at 04:43, Phil Ruffwind r...@rufflewind.com wrote:
I think the error message could be made clearer simply by emphasizing the fact
that type ambiguity over the lack of instances.
Ambiguous type variable 't0' arising from a use of
elem :: a - t0 a - Bool
caused by
On Mon, Aug 3, 2015 at 12:45 PM, Daniel Bergey ber...@teallabs.org wrote:
I thought GHC would infer the type when only one instance is in scope,
at least in some cases, like IsString. But I could well be wrong about
that.
Typeclasses are open-world; this is not a safe assumption, since
Ruffwind; Reid Barton
| Cc: ghc-devs
| Subject: Re: Typechecker / OverloadedStrings question 7.8 vs. 7.10
|
| On 2015-08-03 at 04:43, Phil Ruffwind r...@rufflewind.com wrote:
| I think the error message could be made clearer simply by emphasizing
| the fact
| that type ambiguity over the lack
I think the error message could be made clearer simply by emphasizing the fact
that type ambiguity over the lack of instances.
Ambiguous type variable 't0' arising from a use of
elem :: a - t0 a - Bool
caused by the lack of an instance 'Data.String.IsString (t0 Char)'
Either add
On 2015-07-31 at 08:59, Simon Peyton Jones simo...@microsoft.com wrote:
Daniel Bergey wrote:
| How hard would it be to give a different error message instead of No
| instance ... when the type variable is ambiguous? I always find this
| error slightly misleading, since it seems to me that
On Sun, Aug 2, 2015 at 12:58 PM, Daniel Bergey ber...@teallabs.org wrote:
On 2015-07-31 at 08:59, Simon Peyton Jones simo...@microsoft.com wrote:
Daniel Bergey wrote:
| How hard would it be to give a different error message instead of No
| instance ... when the type variable is
it to say? I think it likely we could make it say that!
S
| -Original Message-
| From: Daniel Bergey [mailto:ber...@teallabs.org]
| Sent: 31 July 2015 02:23
| To: Michael Karg; Simon Peyton Jones
| Cc: ghc-devs
| Subject: Re: Typechecker / OverloadedStrings question 7.8 vs. 7.10
Hi devs,
in the followin snippet:
{-# LANGUAGE OverloadedStrings #-}
import Data.Char (isAlphaNum)
import Data.ByteString.Char8 as BS (all)
main =
print $ check str
where
check = BS.all (\x - x `elem` valid || isAlphaNum x) -- Line 7
valid = $_- -- ::
On 2015-07-30 at 21:39, Michael Karg mgoreme...@gmail.com wrote:
I guess without that pragma, the string literals already imply t ~ [] for
Foldable t.
You're basically right. Without OverloadedStrings, a string literal
(foo) is always a String. With OverloadedStrings, it's free to be
any t
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