Skip to content

GitLab

  • Menu
Projects Groups Snippets
  • Help
    • Help
    • Support
    • Community forum
    • Submit feedback
  • Sign in / Register
  • GHC GHC
  • Project information
    • Project information
    • Activity
    • Labels
    • Members
  • Repository
    • Repository
    • Files
    • Commits
    • Branches
    • Tags
    • Contributors
    • Graph
    • Compare
    • Locked Files
  • Issues 4,869
    • Issues 4,869
    • List
    • Boards
    • Service Desk
    • Milestones
    • Iterations
  • Merge requests 459
    • Merge requests 459
  • CI/CD
    • CI/CD
    • Pipelines
    • Jobs
    • Schedules
    • Test Cases
  • Deployments
    • Deployments
    • Releases
  • Analytics
    • Analytics
    • Value stream
    • 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 Compiler
  • GHCGHC
  • Issues
  • #11352
Closed
Open
Created Jan 04, 2016 by Icelandjack@IcelandjackReporter

Allow applying type to label

{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE FlexibleContexts      #-}
{-# LANGUAGE TypeApplications      #-}
{-# LANGUAGE OverloadedLabels      #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE DataKinds             #-}

import GHC.TypeLits
import GHC.OverloadedLabels

instance IsLabel "answer" Int where
  fromLabel _ = 42

answer :: IsLabel "answer" a => a
answer = #answer

The follow works:

>>> answer @Int
42

but fails with a label:

>>> #answer @Int
<interactive>:...:1: error:
    • Cannot not apply expression of type ‘t0’
      to a visible type argument ‘Int’
    • In the expression: #answer @Int
      In an equation for ‘it’: it = #answer @Int
Trac metadata
Trac field Value
Version 7.10.3
Type FeatureRequest
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
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