#14321: -fsolve-constant-dicts is not very robust when dealing with GADTs -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #9701 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I expected `-fsolve-constant-dicts` to nail #9701, it didn't fire at all but a slightly modified version does. {{{ {-# LANGUAGE GADTs #-} {-# LANGUAGE TypeApplications #-} module Foo where data Silly a where Silly :: Ord a => a -> Silly a isItSilly :: a -> Silly a -> Bool isItSilly a (Silly x) = a < x isItSillyIntTA :: Int -> Silly Int -> Bool isItSillyIntTA = isItSilly @Int isItSillyInt :: Int -> Silly Int -> Bool isItSillyInt a x = isItSilly a x isItSillyInt2 :: Int -> Silly Int -> Bool isItSillyInt2 a (Silly x) = a < x isItSillyInt3 :: Int -> Silly Int -> Bool isItSillyInt3 a (Silly x) = isItSilly a (Silly x) }}} Both versions 2 and 3 specialise nicely using the `Int` `Ord` dictionary. The first two versions don't. I'm unsure whether it *should* fire or not but I am making this ticket to record this fact. Clonable code and core dump - https://gist.github.com/mpickering/f84a5f842861211e8e731c63e82d5c01 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14321 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler