FW: [GHC] #916: windows installer should play nice with other Haskell tools

[Claus Reinke]

> http://haskell.org/haskellwiki/Installers
> 
> Anything there that is either unclear or controversial?

1. possibility to avoid new file type assocs: agreed

2. icon: no opinion

3. file type for .hs/.lhs: 
    all Haskell systems should agree on one (and I have 
    a vague feeling that there was a consensus about this
    several years back, something to do with MIME?)

4. actions: 
    + "open with X" (where X is ghci, hugs, ..): agreed
    + default action: _never_ override existing default!!

so the only unclear/controversial point seems to be the
default. from discussion with Neil, I assume that the 
programmer/installer-perspective is not quite as simple
as the user perspective, but here's what I'd like to see:

a. all installers should agree on the file type for .hs/.lhs
    (currently, they don't)

b. if I decide to permit an installer for X to register itself 
    for .hs/.lhs, it should ensure that the common file type
    is registered, and add a non-default action "Open with X"
    for that file type  

    (by non-default, I mean the actions that are listed in the 
    "Edit File Type" dialogue and are available in right-click 
    menues, but not set as the default action for double-click)

    [as an aside: "Build with ghc --make" might also make 
     sense for the ghc installer; as would version numbers
     for all menu entries, as "Open with GHCi", eg., is not
     uniquely determined if both 6.4.2 and 6.6 are installed]

c. this means that as long as I have any Haskell tool installed,
    .hs/.lhs will be recognized with the common file type and 
    all installed Haskell tools are available from the right-click 
    menu for that file type (provided I've allowed registration),
    happily coexisting.

    if I want to make any of those tools the default, I can 
    do so, without overriding or losing other actions (for me,
    the default will be an editor, for Neil it will be WinHugs
    calling out to an editor, for someone else it might be GHCi..)

in other words, no priorities between tools, no editing via
WinHugs (unless the user sets that as the default). if you 
absolutely insist on making one tool the default handler:

- ask the user before you do so
- don't overwrite the existing default (A), just add an action
    (B) and switch defaults (from A to B), so that both actions
    remain available

unless I've missed something, this will result in happiness
amongst both newbies and oldies:-)

- newbies won't have any old Haskell tools installed,
    will just accept all installer defaults, and will thus end
    up in WinHugs/GHCi/WinHugs Edit/.. via a simple
    double click, depending on what tool they installed

- oldies will keep all their old settings and file type handlers
    available, just gain a new option with every new tool
    they install and lose one with every tool they uninstall

hth,
claus