#9908: Improve enumFromX support for OverloadedLists -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: ekmett Type: feature request | Status: new Priority: normal | Milestone: 7.12.1 Component: Core Libraries | Version: 7.9 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- At present, `OverloadedLists` desugars `[m..n]` as `fromList (enumFromTo m n)`. This is sometimes okay, but terrible for `Data.Sequence`. In particular, I want, for example, {{{#!hs [m..n] :: Seq Int }}} to end up as `fromFunction (n-m+1) (+m)`, which performs much better. There are a few approaches that look reasonable: 1. Try to catch `fromList (enumFromTo m n)` before `enumFromTo` becomes `eftInt`. This does not, unfortunately, seem to work. 2. Grab `eftInt` after it gets written back from `eftIntFB`. This would probably work, but it's currently impossible because `eftInt` is not exported from `GHC.Exts` or even `GHC.Enum`. 3. Add `enumFromTo`, etc., to the `IsList` class. Default to the current behavior, but if possible use `fromListN` for well-known `Enum` types. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9908 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler