#15403: Compact Regions with Lazy Evaluation -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Currently, adding a value to a compact region evaluates it to normal form. I'm wondering if it's possible to have another compacting primitive that can add unevaluated thunks to a compact region. These thunks would be evaluated as they were demanded, and the resulting values would be added to the compact region. I actually have a use case for this in mind involving very large map-like data structures whose size exceeds system memory when in normal form but that are largely unevaluated, giving them a memory footprint that is a fraction of what it would be. One problem would be that a compaction failure (from someone trying to stick a function or a `MutableArray#` into a compact region) would happen after the call to `compactLazy`, so you end up with all the usual lazy IO problems. Another problem would be that the thunks wouldn't get GCed, since they would live in a compact region (and also because you could not update the references to the thunk, since compact regions are not scanned during GC). Neither of these are absolute deal-breakers though. Are there other problems that make this fundamentally impossible to do? Or is this something that could conceivably be added? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15403 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler