#2915: Arity is smaller than need be --------------------------------------------+------------------------------ Reporter: simonpj | Owner: simonpj Type: bug | Status: infoneeded Priority: lowest | Milestone: 7.6.2 Component: Compiler | Version: 6.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime performance bug | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Comment (by simonpj): If we eta-expand to: {{{ h x = let f = \y -> case x of { True -> t1 y; False -> t2 y } in (f,f) }}} then we'd do the `case x` each time we call `f`, rather than once. But in exchange we get better code for `f`. Worth a try perhaps. Notice that we do such things between lambdas: {{{ h x = let g = \y -> case x of { True -> \v->e1; False -> \v->e2 } in ... }}} here we do (already) eta-expand g to {{{ h x = let g = \y v -> case x of { True -> e1; False -> e2 } in ... }}} This seems inconsistent with not doing so in for `f`. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/2915#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler