Hi All,
I was trying to use folds to return the last line of a text file but I
can't to get the behaviour I want. Specifically it seems to run
my fold multiple times instead of once over the whole file.
lastline :: IO ()
lastline = runEffect $ (myFold . view T.lines) T.stdin >-> T.stdout
myFold :: Monad m => FreeT (Producer Text m) m () -> Producer Text m ()
myFold = folds acc "" extract
acc :: Show a => t -> a -> a
acc _ a = trace ("acc " ++ show a) a
extract :: Show a => a -> a
extract a = trace ("extract " ++ show a) a
When running it with a text file containing
1
2
3
The result I get is:
acc "1"
extract "1"
acc "2"
extract "2"
acc "3"
extract "3"
123
When what I expected was:
acc "1"
acc "2"
acc "3"
extract "3"
3
I'm sure I'm doing something silly and I'm guessing it's in this part:
"myFold . view T.lines". If someone is able to point me in the right
direction that would be greatly
appreciated.
cheers
Andrew
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