#2110: Rules to eliminate casted id's -------------------------------------+------------------------------------ Reporter: igloo | Owner: Type: feature request | Status: patch Priority: lowest | Milestone: 7.10.1 Component: Compiler | Version: 6.8.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by nomeata): I changed the definition of `coerce` back to the naive one, and aimed at making the rule matcher smarter. I did this by adding a function `exprIsLambda_maybe` which is used when a rule template contains a lambda. Previously, the code would either use a Lambda, if its there, or eta- expand both sides otherwise. The latter seemed to be somewhat dangerous (could waste work, although I could not produce a example for that due to later CSE and other effects), and did not help in the case discussed here. So instead I try to „make the expression“ into a lambda. Either it already is a lambda, or it is a (nested) application of something that has a currently active unfolding which is unsaturated: In that case, unfold it, `simpleOptExpr` and recursively look for further lambdas. Any any cast occurring while doing so will be pushed inside the lambda. With that change, matching `unsafeCoerce` works as well! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/2110#comment:45 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler