Proposal: Add concatMapM function (#2042)

[Johan Tibell]

On Jan 31, 2008 2:13 PM, Bulat Ziganshin <bulat.ziganshin at gmail.com> wrote:
> Hello Johan,
>
> Thursday, January 31, 2008, 2:35:06 PM, you wrote:
>
> > * Those who do text I/O. We might want to add an encoding parameter to
> > those or add other, identical functions that takes the encoding as a
> > parameter and use a default encoding for the functions that lack
> > explicit encoding. e.g.
>
> >> readFile :: FilePath -> IO String  -- defaults to some encoding
> >> readFileWithEnc :: Encoding -> FilePath -> IO String  -- explicit encoding, should have a better function name
>
> i can quickly tell why it's bad idea. it doubles amount of i/o
> functions just for this particular need. then you will notice that we
> also need functions which don't lock Handle or add some other
> processing and number of functions will double again and again
>
> i don't even say that for practical programming you will quickly find
> that passing encoding for particular file down all the functions that
> work with it is a nightmare
>
> the right way to deal with "modifiers" is to attach them to the Handle
> itself like this:
>
> f <- openFile "name" >>= withLocking >>= withEncoding utf8
>
> and now look at http://haskell.org/haskellwiki/Library/Streams ;)
>
>
> > data Encoding = Ascii | Utf8 | Utf16  -- no ALL CAPS pretty please!
>
> btw, it's another bad idea which means that set of encodings cannot be
> changed without changing library. it will be especially "great" if we
> will hard-code this into base, meaning that in order to get support
> for new encodings you should upgrade your ghc and any new encodings
> will become available for ghc users ONE YEAR AFTER actual implementation
>
> in FP language, the best way to provide encoding is to define it as
> pair of functions:
>
> data Encoding = Encoding { encode :: String -> String
>                          , decode :: String -> String }
>
> utf8 = Encoding encodeUtf8 decodeUtf8

Just to be clear here. I don't care (for the purpose of this email)
what these functions will look like. I just provided some random
examples. I was asking how changes to existing functions would be
handled. It's interesting to hear your ideas on the topic none the
less. :)

-- Johan