[Haskell-cafe] Those damned parentheses

[Yitzchak Gale]

Eitan Goldshtrom wrote:
>> f p = putStrLn $ (show (Main.id p)) ++ " - message received"

Brandon S Allbery KF8NH wrote:
> f p = putStrLn $ (show $ Main.id p) ++ " = message received"

wren ng thornton <wren at freegeek.org> wrote:
>    f p = putStrLn $ show (Main.id p) ++ " - message received"
>    f p = putStrLn $ (show . Main.id) p ++ " - message received"
>    f p = putStrLn $ ((show . Main.id) p) ++ " - message received"
>    f p = putStrLn $ (show . Main.id $ p) ++ " - message received"
>    f p = putStrLn ((show . Main.id $ p) ++ " - message received")
> etc.

I think the clearest way to write it is:

f = putStrLn . (++ " - message received") . show . Main.id

Not because it happens to be point-free, but because it is
the "combinator" approach. You apply functions one after
the other, each with its own simple meaning and purpose.

If I were to describe to someone in words what this
function does, I would say something like: "Apply Main.id,
turn it into a string, tack a message onto the end, and
print it." So why not write it that way in Haskell?

One of the nicest features of Haskell is that the
combinator approach is often so natural.

Regards,
Yitz