[Haskell-cafe] Imports at bottom, why not?

[Thiago Negri]

Appending code to a module via script is a valid use case, but then you
just use top imports. This doesn't make a point towards forbidding bottom
imports.

The point is: there are a number of reasons to do top imports and another
number of reasons to do bottom imports. I think bottom imports could be
very useful. Even literate Haskell could read better with bottom imports,
in my opinion.
Em 22/04/2014 19:09, "Ivan Lazar Miljenovic" <ivan.miljenovic at gmail.com>
escreveu:

> On 23 April 2014 04:28, Niklas Haas <haskell at nand.wakku.to> wrote:
> > On Tue, 22 Apr 2014 14:59:44 -0300, Thiago Negri <evohunz at gmail.com>
> wrote:
> >> When reading code, I find it quite distracting to have to get past the
> >> import list to reach the actual module code, as the import list can be
> (and
> >> often is) quite big.
> >>
> >> So, why not issue import statements at the bottom of a module file?
> >>
> >> Likewise, we can use "where" statements to define names used in a
> function
> >> after using them, so they don't distract the reader.
> >>
> >> I'm against imports at the middle of the file.
> >> But I guess being able to issue them at the end of the module could make
> >> sense if you want to get the reader straight to the code.
> >>
> >> A language pragma could be used to select between top imports or bottom
> >> imports (can't use both).
> >>
> >> What do you think?
> >>
> >> Example:
> >>
> >> """
> >> {-# LANGUAGE LateImports #-}
> >> module Foo where
> >>
> >> bar :: String
> >> bar = "quux"
> >>
> >> baz :: Fiz
> >> baz = mkFiz
> >>
> >> import Fiz (Fiz, mkFiz)
> >> """
> >
> > A practical reason is that this lets you process modules dependency
> > graphs without ever analyzing the structure past the import list.
>
> Also so when you're reading the code you have an idea up-front of what
> kind of external modules it might be using; otherwise - especially if
> the names are generic (e.g. "Parser") or using some form of overloaded
> extension (e.g. OverloadedStrings) - you might not be able to tell as
> easily the behaviour of the code.
>
> After all, two different parser libraries might behave differently
> (how they deal with backtracking is usually a big difference), and if
> you see someone using OverloadedStrings with ByteStrings then you know
> to be more careful about the code if using characters not expressable
> in a single byte.
>
> Whilst I doubt this is a common use-case in practice, it's also
> possible someone might want to add some code to a file using a shell
> script: if the imports are at the top you can just append it; if the
> imports are at the bottom you have to be more careful.
>
> --
> Ivan Lazar Miljenovic
> Ivan.Miljenovic at gmail.com
> http://IvanMiljenovic.wordpress.com
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