[Haskell-cafe] [Haskell-beginners] Why is the the transpose function in Data.List more complicated?
garious at gmail.com
Sat Aug 4 02:05:10 CEST 2012
> transp :: [[b]] -> [[b]]
> transp (:_) = 
> transp rows = map head rows : transp (map tail rows)
> Why is the the transpose function in Data.List more complicated?
In the Data.List version, the list comprehension syntax quietly
filters out items that fail to pattern-match (empty lists). Therefore
the transpose in Data.List does not generate a pattern-match exception
when you give it lists of different lengths:
transpose [, , ] == [[1,3]]
The Data.List version also returns an empty list if the input is an
empty list, whereas your version returns an infinite list of empty
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