#12513: Template Haskell boxes singleton unboxed tuples when splicing them -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Template | Version: 8.0.1 Haskell | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC accepts Unknown/Multiple | invalid program Test Case: | Blocked By: Blocking: | Related Tickets: #5332 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- As noticed [https://phabricator.haskell.org/D2448#71603 here], this program somehow compiles: {{{#!hs {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE UnboxedTuples #-} module Bug where import Language.Haskell.TH.Lib import Language.Haskell.TH.Ppr import Language.Haskell.TH.Syntax f :: $([t| (# Int #) |]) -> Int f x = x g :: $(unboxedTupleT 1 `appT` conT ''Int) -> Int g x = x }}} Despite the fact that `(# Int #)` and `Int` are most definitely //not// the same type! If you compile with `-ddump-splices`, you'll see what's going on: {{{ $ /opt/ghc/head/bin/ghc Bug.hs -ddump-splices [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:12:8-40: Splicing type unboxedTupleT 1 `appT` conT ''Int ======> Int Bug.hs:9:8-23: Splicing type [t| (# Int #) |] ======> In }}} It appears that the splicing machinery is turning `(# Int #)` into `Int` behind the scenes. Luckily, this should be easy to fix. Patch coming soon. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12513 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler