[Haskell-cafe] Does somebody know about these functions?
holmisen at gmail.com
Tue Feb 28 18:06:25 CET 2012
Two functions that I see useful are described here and I would like to
know if they are defined in some more or less standard Haskell
library. Hoogle (http://www.haskell.org/hoogle) did not reveal
anything about that.
Function 'inter' applies given function to each succeeding pair of
elements of a list.
inter :: (a -> a -> b) -> [a] -> [b]
inter f  = 
inter f l = map (uncurry f) $ zip l (tail l)
and $ inter (<=) l -- checks if 'l' is ordered
inter (,) l -- gives succeeding pairs
Function 'withPair' takes a pair and applies a function to it's first
element, another function to it's second element and finally combines
the results with yet another function.
withPair :: (a' -> b' -> c) -> (a -> a') -> (b -> b') -> (a,b) -> c
withPair f fa fb (a,b) = fa a `f` fb b
words  = 
words s = withPair (:) id words (break isSpace $ dropWhile isSpace s)
lines  = 
lines s = withPair (:) id lines (break (== '\n') s)
mapPair = withPair (,)
This function can abstract away the (in my opinion ugly) pattern (as
seen in the examples):
foo list = let (a,b) = <somefun> list in <somefun2> a `<combinedWith>` foo b
Anyone knows about these two functions or variants thereof?
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