Not in scope [GHC-76037]

An identifier can only be used if it is in scope; i.e. if it is bound or declared previously and that binding/declaration is available at the usage location.

Examples

Unbound data constructor in lambda

The data constructor A used in the lambda expression is not in scope.

Error Message

NotInScopeLambda.hs:3:6: error: [GHC-76037]
    Not in scope: data constructor ‘A’
  |
3 | f = \A -> A
  |      ^

NotInScopeLambda.hs

Before

module NotInScopeLambda where

f = \A -> A

After

module NotInScopeLambda where

data Foo = A | B

f :: Foo -> Foo
f = \A -> A

Unbound class name

The class name B referenced in the definition of class C is not in scope.

Error Message

NotInScopeClass.hs:3:8: error: [GHC-76037]
    Not in scope: type constructor or class ‘B’
  |
3 | class (B a) => C a where
  |        ^

NotInScopeClass.hs

Before

module NotInScopeClass where

class (B a) => C a where
 op1 :: a -> Int

After

module NotInScopeClass where

class B a where
  op :: a -> a

class (B a) => C a where
 op1 :: a -> Int

Data constructor not imported

The import statement import Foo (Bar) imports the Bar data type, but not its constructor MkBar. As such, the constructor is not in scope.

Error Message

IncorrectImport.hs:6:12: error: [GHC-76037]
    Not in scope: data constructor ‘MkBar’
  |
6 | barAddOne (MkBar n) = MkBar (n + 1)
  |            ^^^^^

IncorrectImport.hs

Before

module IncorrectImport where

import Foo (Bar)

barAddOne :: Bar -> Bar
barAddOne (MkBar n) = MkBar (n + 1)

After

module IncorrectImport where

import Foo (Bar(..))

barAddOne :: Bar -> Bar
barAddOne (MkBar n) = MkBar (n + 1)

Field selector exported with NoFieldSelectors

Error Message

NoFieldSelectorsExport.hs:3:35: error: [GHC-76037]
    Not in scope: ‘foo’
    Suggested fix:
      Notice that ‘foo’ is a field selector belonging to the type ‘T’
      that has been suppressed by NoFieldSelectors.
  |
3 | module NoFieldSelectorsExport (T, foo) where
  |                                   ^^^

Explanation

The field selector foo has been disabled via NoFieldSelectors, therefore it cannot be a top-level export. The fix is to export it as part of its type T (consequently it can be imported for e.g. record creation or updates).

NoFieldSelectorsExport.hs

Before

{-# LANGUAGE NoFieldSelectors #-}

module NoFieldSelectorsExport (T, foo) where

data T = MkT { foo :: T }

After

{-# LANGUAGE NoFieldSelectors #-}

module NoFieldSelectorsExport (T (foo)) where

data T = MkT { foo :: T }