[Haskell-cafe] How to write fast for loops

Niklas Hambüchen mail at nh2.me
Sun Apr 27 01:16:06 UTC 2014

Hey John,

do you mean something along the lines of `V.forM_ (fromList [1..n])`?
I guess GHC wouldn't mash away the list in this case and I'd have to 
use the new OverloadedLists with `V.forM_ [1..n]` (indeed that looks 
quite sweet).
However, would that actually be fast? Judging from how list syntax is 
desugared, I guess that would use `V.enumFromTo` then, whose docs claim 
"WARNING: This operation can be very inefficient. If at all possible, 
use enumFromN instead".

Does anybody know  wonder if "vector literals" desugar enumFromN, or 
what "can be very inefficient" means?


On Sun 27 Apr 2014 01:13:52 BST, John Lato wrote:
> I usually use a manually written loop, but you can use Data.Vector for
> this and it should fuse.

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