#10225: GHC does not specialize based on type equality -------------------------------------+------------------------------------- Reporter: yongqli | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Description changed by yongqli: Old description:
Based on my testing, it seems that if I have a function like
f :: (v ~ V2) => v -> v
this will be slower than
f :: v -> v
It would be great if GHC could do this optimization. The reason I want this is that I have written some very generic functions in my program, which are actually only used for one type. SPECIALIZE doesn't seem to do enough, as it's hard to get those GHC to "see" all of those types. As a compromise, I tried to tell GHC what those types actually are via type equalities, so that I can keep type constraints around for the future.
New description: Based on my testing, it seems that if I have a function like f :: (v ~ V2) => v -> v this will be slower than f :: V2 -> V2 It would be great if GHC could do this optimization. The reason I want this is that I have written some very generic functions in my program, which are actually only used for one type. SPECIALIZE doesn't seem to do enough, as it's hard to get those GHC to "see" all of those types. As a compromise, I tried to tell GHC what those types actually are via type equalities, so that I can keep type constraints around for the future. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10225#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler