GHC error message on type mismatch

David Fox dsf at seereason.com
Thu Nov 7 14:21:03 UTC 2013


It *is* sometimes difficult to remember that my expectations and I are not
part of this equation - it might be a better prompt to say something like

   type mismatch between function parameter and supplied value:
      function parameter type: A
      supplied value type: B


On Thu, Nov 7, 2013 at 6:02 AM, Simon Peyton-Jones <simonpj at microsoft.com>wrote:

> The motivation is this. Consider
>
>         f True
>
> where f :: Int -> Char
>
> Then
>   f *expects* an argument of type Int
>   but the *actual* argument has type Bool
>
> Does that help?
>
> Simon
>
> | -----Original Message-----
> | From: Glasgow-haskell-users [mailto:glasgow-haskell-users-
> | bounces at haskell.org] On Behalf Of David Luposchainsky
> | Sent: 07 November 2013 12:23
> | To: Daniel Trstenjak; glasgow-haskell-users at haskell.org
> | Subject: Re: GHC error message on type mismatch
> |
> | On 2013-11-07 12:52, Daniel Trstenjak wrote:
> | > My problem is with 'Expected' and 'Actual', that I'm often unsure if
> | > the compiler is "expecting" something or if I'm the expecting one
> | > and the same goes for "actual".
> |
> | Funny you mention it; I think I just got too used to the fact that every
> | time I see this error I have to take a step back to remember what it
> | means exactly. Renaming it to "given" or "provided" would really help.
> |
> | +1
> |
> | David
> |
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