-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 7/2/10 07:23 , Vincent Hanquez wrote:
I'm not sure exactly what the API would looks like, but I think basically you would enter/leave the state monad quite frequently in incremental mode, since the whole point of the incremental api is having this context built partially. for this reason, you end up with something really close to explicit state keeping, isn't it ?
You can do this if you need to (execState) but it's better to wrap the whole thing in a State monad. Think of it this way: (flip runState) can be read as "withContext":
flip runState initContext $ do -- do stuff, invoking update as needed to build the state
Although now that I think about it, if we're just appending to the state, this should possibly be a Writer instead of a State; the interface is simpler. Or to try to be a little more concrete about it:
type HashContext = String
-- build up a hash context incrementally, then hash it hashWithContext :: () -> Hash hashWithContext = hash . execWriter
-- add a chunk to the hash context addToHash :: String -> Writer HashContext () addToHash = tell
-- use it messageHash = hashWithContext $ do -- do something addToHash aLine -- doSomethingElse foldM addToHash [aListOfStuff] -- ...
- -- brandon s. allbery [linux,solaris,freebsd,perl] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkwt/z0ACgkQIn7hlCsL25Uz5wCeO9db+eqE/azqoEgJ3L3vQJzF XKEAn0I8rEzf0tQfylc3pGq4+E6V4M72 =C/BN -----END PGP SIGNATURE-----