As other people have mentioned, you are duplicating library
functionality. But nobody has actually talked about the performance
characteristics of your code.
Fortunately for you, the calls to (++) in your recursion are
right-associative, so you don't have an asymptotic problem where your
program gets slower and slower for large inputs; it should stay
linear.
But you are wasting some work. In particular, (concat (intersperse "
" l)) produces a String, and then (++) duplicates all of the cons
cells in that string as it rebuilds it so that the tail connects with
the next string.
So there is a potential benefit to using a difference list, albeit
only by around a 2x factor.
-- ryan
On Sat, Feb 6, 2010 at 4:42 AM, Mark Spezzano
Hi,
Just wondering whether I can use ShowS or tupling or Difference Lists to speed up the following code?
It's basic text processing. It takes in a list of Lines where each Line is a list of Words and intersperses " " between them then concatenates them into a longer String. Note that there is a recursive call and the ++ operator.
Thanks
Mark
-- Function: joinLines -- Joins the Words within Lines together with whitespace and newline characters -- Argument: Lines to pad with whitespace and newlines -- Evaluate: The processed and concatenated String joinLines :: [Line] -> String joinLines (l:[]) = concat (intersperse " " l) joinLines (l:ls) = (concat (intersperse " " l)) ++ ('\n':joinLines ls)
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