#15534: Allow associated types in Minimal pragmas -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Missing associated type definitions can cause compile-time problems similar to the run-time problems that occur when necessary methods are missing. {{{#!hs {-# language TypeFamilies, UndecidableInstances #-} class Foo a where type X a type X a = Y a type Y a type Y a = X a instance Foo Int bob :: X Int bob = undefined }}} Compiling this gives {{{ Minim.hs:14:7: error: • Reduction stack overflow; size = 201 When simplifying the following type: Y Int Use -freduction-depth=0 to disable this check (any upper bound you could choose might fail unpredictably with minor updates to GHC, so disabling the check is recommended if you're sure that type checking should terminate) • In the expression: undefined In an equation for ‘bob’: bob = undefined | 14 | bob = undefined }}} That's not exactly the best error message in the world. I would like to be able to write {{{#!hs {-# MINIMAL X | Y #-} }}} which would mean that instances should give type instances for `X` or `Y`. I don't see any reason to prohibit mixing associated types and methods in a single `MINIMAL` pragma. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15534 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler