#15928: Reduction stack overflow when using "coerce" -------------------------------------+------------------------------------- Reporter: harendra | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.3 Component: Compiler | Version: 8.6.2 Resolution: | Keywords: Operating System: MacOS X | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by harendra): I am further puzzled, as we know already, this definition works fine: {{{ data Stream m a = Stream { unStream :: forall r. (Stream m a -> m r) -> m r } }}} And this one results in an error: {{{ data Stream (m :: * -> *) a = Stop | Yield a (Stream m a) }}} {{{ xy.hs:26:20: error: • Couldn't match representation of type ‘a0’ with that of ‘a’ arising from a use of ‘coerce’ ‘a’ is a rigid type variable bound by the type signature for: f :: forall a. SerialT Identity a -> Identity Bool at xy.hs:25:1-40 • In the second argument of ‘(.)’, namely ‘coerce’ In the second argument of ‘(.)’, namely ‘idSerial . coerce’ In the expression: g . idSerial . coerce • Relevant bindings include f :: SerialT Identity a -> Identity Bool (bound at xy.hs:26:1) | 26 | f = g . idSerial . coerce | ^^^^^^ }}} If there is no bug then this needs to be explained in some simple way. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15928#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler