[darcs-devel] [issue1895] create a customised monad for Darcs to do IO in

[Ganesh Sittampalam]

New submission from Ganesh Sittampalam <ganesh at earth.li>:

We should replace direct use of the IO monad in Darcs with a customised 
monad that abstracts away various things. This is important to make the 
Darcs library properly usable.

 - The use of global IORefs (use ReaderT instead? - still with IORefs, 
but not ones defined using the global variables hack)
 - The use of exit/exitWith and atexit handlers (replace with a custom 
exception type and finally blocks?)
 - (perhaps) things like progress reports
 - The mechanism for working with directories (see issue1774 and related 
discussion)
 - output to stdout/stderr
 - (perhaps) all the other IO Darcs does

A good starting point would be to newtype wrap the IO monad, and 
implement MonadIO. The downside is that this would involve putting 
liftIO in all over the place, which would be quite ugly, but the 
advantage is that it would be essentially mechanical.

Once that's in place we could gradually move things into the monad.

One thing to keep a close eye at each step on would be performance.

----------
messages: 11805
nosy: dmitry.kurochkin, ganesh
status: need-implementation
title: create a customised monad for Darcs to do IO in
topic: Core, Library

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