On Tue, 2009-02-24 at 13:57 +0100, Christian Maeder wrote:
Duncan Coutts wrote:
Manipulating Entries is also not a typical user task. (Maybe the type Entries should just be "[Either String Entry]", but the given type is fine, as it only allows a final failure string)
Yeah I think only one failure is good.
data Entries = Entries [Entry] (Maybe String) or directly using "([Entry], Maybe String)"
Sadly that does not account for streaming. We may not discover the error until we've processed 100 megabytes of tar file. So we cannot give top level access to an error that might happen at the end.
is an alternative, where "Nothing" indicates no failure. This would avoid the extra folding and mapping on Entries
The nice thing about the current Entries is that it models the failure modes and works lazily.
and maybe "unpack" could then work on [Entry] only.
True, though it's also convenient that unpack just raises any entry errors as IO errors. Converting Entries to [Entry] requires reading the whole thing (to check there are no errors), again defeating lazyness/streaming which would mean we could not work with large tar files in constant space. Duncan