Not in scope data constructor

  • Module names start with a capital - Haskell is case sensitive
  • Line up your code at the left margin - layout is important in Haskell.
  • The bit in brackets is the export list - miss it out if you want to export all the functions, or put everything you want to export in it.

First.hs:

module First where

type S = SetType
data SetType = S[Integer]

Second.hs:

module Second where
import First


module first () where

Assuming in reality the module name starts with an upper case letter, as it must, the empty export list - () - says the module doesn't export anything, so the things defined in First aren't in scope in Second.

Completely omit the export list to export all top-level bindings, or list the exported entities in the export list

module First (S, SetType(..)) where

(the (..) exports also the constructors of SetType, without that, only the type would be exported).

And use as

module Second where

import First

foo :: SetType
foo = S [1 .. 10]

or, to limit the imports to specific types and constructors:

module Second where

import First (S, SetType(..))

You can also indent the top level,

module Second where

    import First

    foo :: SetType
    foo = S [1 .. 10]

but that is ugly, and one can get errors due to miscounting the indentation easily.

Tags:

Haskell

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