• bearophile (29/29) Mar 17 2011 I've suggested to add to Phobos functions like amap(), sum(), better max...

bearophile <bearophileHUGS lycos.com> writes:

I've suggested to add to Phobos functions like amap(), sum(), better
max()/min(), and maybe afilter() too. amap() means array(map()), sum() is
similar to reduce!q{a+b}(), and the max() I have suggested is similar to
reduce!max().

Notes:
- Functions like sum() are used all the time, Python programmers use it
thousands of times.
- In some situations a specialized version is faster, I have shown this about
sum() in an enhancement request (Andrei has then tried to generalize this
suggestion of mine again);
- array(map()) uses twice the number of parentheses of amap(). Haskell syntax
shows very well why too many parentheses make functional-style code needlessly
harder to read.
- Experience shows me that in D you can't use lazy things as much as you use in
Haskell. This means that very often I have to convert the results of D
map()/filter() to true arrays.
- sum() is a semantic chunk, while reduce!q{a+b}() is not as explicit in its
purpose, it's not a single chunk. You are able to speed up your coding if you
need to use less chunks.
- The number of "nearly duplicated" functions to add is quite limited.

But such functions aren't orthogonal, you can build them with few other small
things. In Python std library you see functions that aren't orthogonal, but
they are handy, like ifilterfalse() and starmap():
http://docs.python.org/library/itertools.html

You see something similar in the Haskell Prelude (it's a standard module loaded
and compiled before any other), a very well designed piece of code:
http://www.haskell.org/onlinereport/standard-prelude.html

It contains un-orthogonal functions like:

concatMap :: (a -> [b]) -> [a] -> [b]
concatMap f = concat . map f


zipWith          :: (a->b->c) -> [a]->[b]->[c]
zipWith z (a:as) (b:bs)
                 =  z a b : zipWith z as bs
zipWith _ _ _    =  []


zip              :: [a] -> [b] -> [(a,b)]
zip              =  zipWith (,)


putStrLn   :: String -> IO ()
putStrLn s =  do putStr s
                 putStr "\n"
   

print      :: Show a => a -> IO ()
print x    =  putStrLn (show x)

Bye,
bearophile