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Today's Topics:
1. Re: IO operations (鲍凯文)
----------------------------------------------------------------------
Message: 1
Date: Thu, 13 Aug 2020 18:23:02 -0700
From: 鲍凯文 <traqueofzi...@gmail.com>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] IO operations
Message-ID:
<camjcg+etzehz66ep0axqxa4ygslx-g9n89m7mcc_g7604yj...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
> * Couldn't match expected type `t0 Char' with actual type `Char'
> * In the second argument of `elem', namely `x'
> In the second argument of `($)', namely '-' `elem` x
> In the expression: not $ '-' `elem` x
Hope the other answers helped. FWIW, just wanted to point out that for me
these kinds of error messages sometimes used to be confusing since the type
of `elem` is `(Foldable t, Eq a) => a -> t a -> Bool`, so the typechecker
tells you it wants to unify `t0 Char` (where `t0` is something `Foldable`)
with `Char`. As Mr. Klink wrote, it looks like you wanted `t0` to be `[]`;
I used to get confused since I was only working with lists and the extra
`Foldable` genericity made it harder to see that I was still just working
with lists.
Best,
toz
>
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