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`UnsupportedRoleDeclaration` Error

errors/UnsupportedRoleDeclaration.md

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Original Source

UnsupportedRoleDeclaration Error

Example

purescript
module ShortFailingExample where

class C a
type role C representational
purescript
module ShortFailingExample where

data D a = D a

type S a = D a
type role S nominal

Cause

A role declaration is provided for a type synonym or a type class.

Fix

  • Remove the role declaration or provide a role declaration for the underlying type of the synonym instead:
diff
 data D a = D a
+type role D nominal
 
 type S a = D a
-type role S nominal