last is not a good consumer
The profiler indicates that print $ last [(1::Int)..10^7] (compiled with -O2) allocates around 8*10^8 bytes. Using the Henning Thienemann-inspired
myLast = fromJust . foldr (\x -> Just . maybe x id) Nothing(based on his code for viewR/unsnoc) reduces allocation by about half at the cost of some extra work. What we really want, I believe, is for last to fuse with the producer in a fashion that allows the Ints to be unboxed, eliminating all the allocation. I have no idea if this will fall out of the general fusion work planned for 7.9.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.8.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | libraries/base |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | ekmett, hvr |
| Operating system | |
| Architecture |