Proposal: Add concatMapM function (#2042)

[Johannes Waldmann]

Bulat Ziganshin wrote:

(very sound software engineering arguments -
can someone with The Force please copy Bulat's mail
to Haskell/Category/Style ...)

I agree completely, and just add one remark here :

> data Encoding = Encoding { encode :: String -> String
>                          , decode :: String -> String }
> 
> utf8 = Encoding encodeUtf8 decodeUtf8

this is in fact a method table (Java speak) or a dictionary
(Haskell), and Encoding is the interface (class) -

except that we can have local instances
by passing around dictionaries explicitly.

This is similar to passing a Comparator object
to some sorting routine.

Best regards, Johannes.

PS: go read any honest OO book on the benefits of interface
oriented design - they know this stuff - they got there
the hard way (that is, via C++ :-)