module Example (foo) where

data Bar

foo :: Bar -> Bar
foo x = x

This error occurs when one name is exported, but exporting that name requires some other name(s) to also be exported.

The example above generates the following error:

Error in module M:

An export for foo requires the following to also be exported:

Bar

PureScript requires any types appearing inside a type declaration to also be exported. Similar restrictions apply to things like type classes and type class member exports.

• Follow the instructions in the error, and add the required names to the list of exports:

  module Example (foo, Bar) where
  
  data Bar
  
  foo :: Bar -> Bar
  foo x = x

See the language guide page on modules.