I came up with the same
foo :: Int -> Pipe Int (Maybe Int, Int) IO ()
foo n = loop (Seq.replicate n Nothing) where
loop s = do x <- await
let s' :> a = viewr s
yield (a,x)
loop (Just x <| s')
modulo a tasteless pattern match.
Maybe I should start a different thread, but what bugged me about it was
the `printer` bit.
When we have a very fast process that prints, it all goes to fast for my
terminal to
handle. So I looked a little into builders. I looked at the
conduit-blaze-builder package
without much light; in the end I made a little beginning at figuring out
the Builder and
Builder.Internal modules of more recent `bytestring` s.
The following is very rough and only defines pipes :: `Pipes Builder
ByteString IO r`
when I was hoping for `Consumer ByteString IO r` and the like. and since it
uses
new bytestrings, Gabriel might not be able to test it:
https://github.com/michaelt/pipes-builder-shabby
>
I ran Daniels program 3 ways in test/Test.hs
- once with `for pipe (lift.print)` ("printer");
- once for `for (pipe >-> buildPair) (lift . hPutBuilder stdout)` where
`buildPair` was a simple pipe for showing-in-terms-of-builders
without mediation of strings ("builder")
- once with "simple :: Pipe Builder IO ByteString" as
`for (pipe >-> buildPair >-> simple) (lift . B.putStr)` ("simple")
-- time ./test 1000000 program (> /dev/null)
-- shabby 0m3.517s 0m0.605s
-- builder 0m9.532s 0m0.565s
-- printer 0m10.864s 0m1.340s
-- time ./test 5000000 program
-- shabby 0m18.894s 0m2.734s
-- builder 0m48.195s 0m2.927s
-- printer 0m55.615s 0m6.631s
The first column has the program spilling into stdout,
the other into /dev/null. The backlog gets worse the
longer the program, so though when sent to /dev/null
a straightforward use of builder seems no better,
when sent to stdin it is increasingly crushed by
'proper' -- or so far shabby -- use of builders.
I'm not sure what to make of it. Maybe it could use more study.
Michael
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