Glasgow-haskell-users digest, Vol 1 #816 - 1 msg

George Russell
Tue, 20 May 2003 19:14:43 +0200

Hal Daume wrote a lot, including the following.
> More seriously, I think the idea of going to and from lists of Word8 is
> going to kill performance.  Especially if you are going to write to a file
> in the end.  You're going to have to go:
>   data structure -> [Word8] -> File
> and likely the middle won't be deforested by any compiler.  Whether you
> use functional arrays or lists is somewhat irrelevant -- functional arrays
> are also exceedingly slow.
I completely agree that going via lists of Word8's is unacceptable.  My design
does not require this.  An array of Word8's can be written or read to a file
in a single operation (not counting the length, which needs to be communicated
some other way).

When you need to write to an intermediate data structure, the most efficient
implementation would probably be to write directly to an array, which you realloc
as necessary.  This could be wrapped up into a single pure operation of type
    ::  HasBinaryWrite a => a -> Bytes
(say).  Of course you would need to use IO in the middle, since it happens
that the current interfaces to blocks of reallocable bytes require IO, but
I don't really see how that can be avoided, and the end-user doesn't have
to see it.