Skip to content
GitLab
Projects Groups Topics Snippets
  • /
  • Help
    • Help
    • Support
    • Community forum
    • Submit feedback
  • Register
  • Sign in
  • GHC GHC
  • Project information
    • Project information
    • Activity
    • Labels
    • Members
  • Repository
    • Repository
    • Files
    • Commits
    • Branches
    • Tags
    • Contributor statistics
    • Graph
    • Compare revisions
    • Locked files
  • Issues 5.5k
    • Issues 5.5k
    • List
    • Boards
    • Service Desk
    • Milestones
    • Iterations
  • Merge requests 638
    • Merge requests 638
  • CI/CD
    • CI/CD
    • Pipelines
    • Jobs
    • Artifacts
    • Schedules
    • Test cases
  • Deployments
    • Deployments
    • Releases
  • Packages and registries
    • Packages and registries
    • Model experiments
  • Analytics
    • Analytics
    • CI/CD
    • Code review
    • Insights
    • Issue
    • Repository
  • Wiki
    • Wiki
  • Snippets
    • Snippets
  • Activity
  • Graph
  • Create a new issue
  • Jobs
  • Commits
  • Issue Boards
Collapse sidebar
  • Glasgow Haskell CompilerGlasgow Haskell Compiler
  • GHCGHC
  • Issues
  • #4135

Can't Quote Instance Associated Types in Template Haskell

Give this a whirl:

{-# LANGUAGE TypeFamilies,TemplateHaskell #-}
module Bug where

    class C a where
        type T a

    $([d|  
        instance C (Maybe a) where
            type T (Maybe a) = Char
        |])
$ ghc -c Bug.hs 
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
Loading package array-0.3.0.0 ... linking ... done.
Loading package containers-0.3.0.0 ... linking ... done.
Loading package pretty-1.0.1.1 ... linking ... done.
Loading package template-haskell ... linking ... done.

Bug.hs:7:6:
    Type indexes must match class instance head
    Found `Maybe a[aMy]' but expected `Maybe a[aMx]'
    In the associated type instance for `T'
    In the instance declaration for `C (Maybe a[aMx])'
[glastonbury:~/Projects/Haskell/Truth/Core]$ 
Trac metadata
Trac field Value
Version 6.12.1
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Template Haskell
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information
Assignee
Assign to
Time tracking