error-messages
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haskell
For this example code -- ```haskell {-# LANGUAGE GADTs #-} data T where X :: T Y :: a -> T f :: T -> () f X = ()...
Recently, [Luke McCartney on discourse](https://discourse.haskell.org/t/creating-functor-class/8514) was confused by a bad error message. He wrote this code: ```haskell import Prelude hiding (map, Maybe, Nothing, Just, (), liftA2) class Functor f =>...
When debugging an error it is very important to identify the "speaker" who emitted the error message. For example, I recently had to figure out which tool causes the following...
In the program below, `c` is not in scope where `a` is defined because of the intervening TH splice. The error message in 8.10 was helpful ``` test18.hs:6:5: error: •...
I just encountered this one: ```haskell import Data.Primitive.SmallArray import Data.Primitive.PrimArray import Data.Primitive (Prim) smallToPrim :: Prim b => (a -> b) -> SmallArray a -> PrimArray b smallToPrim f xs...
I got inspired to write this after watching [this video about teaching Haskell to kids](https://www.youtube.com/watch?v=uTmQ_JtjHgw). I am now convinced Haskell's error messages could be improved greatly and I have very...
``` ghci> data T = MkT ghci> MkT :2:1: error: • No instance for (Show T) arising from a use of ‘print’ • In a stmt of an interactive GHCi...
# Summary I think there's some room for improvement for error messages on top level declarations[^1] (module, import). [^1]: Also the word 'top level declaration' could be made more helpful...
In GHC 9.0 and below, the following code would produce an error message that mentions the phrase `type variable 's' would escape its scope`. ```hs runST (newSTRef 5) ``` ```...
 Perhaps something like "Help us improve error messages in Haskell tooling!"
