#7021: Tuple (and other exotic predicates) not yet handled in Template Haskell -------------------------+------------------------------------------------- Reporter: | Owner: goldfire | Status: new Type: | Milestone: 7.8.1 feature request | Version: 7.5 Priority: | Keywords: ConstraintKinds normal | TemplateHaskell Component: | Architecture: Unknown/Multiple Template Haskell | Difficulty: Unknown Resolution: | Blocked By: Operating System: | Related Tickets: Unknown/Multiple | Type of failure: | None/Unknown | Test Case: | Blocking: | -------------------------+------------------------------------------------- Comment (by yoeight): Here's an implementation by introducing a new TH.Pred data constructor (let's say TypeT) as suggested by Richard [http://www.haskell.org/pipermail/ghc-devs/2014-January/003629.html here]: So, this is what I have in mind {{{#!haskell TypeT Type }}} By using the description's snippet, I got: {{{ VarI Tuple.foo (ForallT [PlainTV a_1627398569] [TypeP (AppT (AppT (TupleT 2) (AppT (ConT GHC.Show.Show) (VarT a_1627398569))) (AppT (ConT GHC.Read.Read) (VarT a_1627398569)))] (VarT a_1627398569)) Nothing (Fixity 9 InfixL) }}} What do you think ? Richard also suggested that we could make Pred a type synonym of TH.Type. Unfortunately, I have no idea how to express equality constraint only by using TH.Type -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7021#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler