[Haskell-cafe] Contributing to http-conduit

[Myles C. Maxfield]

Alright. I'll issue another pull request to you when it's done (expect in a
couple weeks).

Thanks for your input so far, Aristid and Michael.

@Chris Wong: Do you want to talk about the Suffix List stuff some time?

--Myles

On Mon, Feb 6, 2012 at 10:14 PM, Michael Snoyman <michael at snoyman.com>wrote:

> +1
>
> On Mon, Feb 6, 2012 at 11:16 PM, Aristid Breitkreuz
> <aristidb at googlemail.com> wrote:
> > I would say: if it adds no package dependencies, put it right in.
> >
> > Aristid
> >
> > Am 06.02.2012 22:09 schrieb "Myles C. Maxfield" <
> myles.maxfield at gmail.com>:
> >>
> >> After all these commits have been flying around, I have yet another
> >> question:
> >>
> >> the 'HTTP' package defines Network.Browser which is a State monad which
> >> keeps state about a "browser" (i.e. a cookie jar, a proxy, redirection
> >> parameters, etc.) It would be pretty straightforward to implement this
> kind
> >> of functionality on top of http-conduit.
> >>
> >> I was originally going to do it and release it as its own package, but
> it
> >> may be beneficial to add such a module to the existing http-conduit
> package.
> >> Should I add it in to the existing package, or release it as its own
> >> package?
> >>
> >> --Myles
> >>
> >> On Mon, Feb 6, 2012 at 12:15 AM, Michael Snoyman <michael at snoyman.com>
> >> wrote:
> >>>
> >>> Just an FYI for everyone: Myles sent an (incredibly thorough) pull
> >>> request to handle cookies:
> >>>
> >>> https://github.com/snoyberg/http-conduit/pull/13
> >>>
> >>> Thanks!
> >>>
> >>> On Sun, Feb 5, 2012 at 8:20 AM, Myles C. Maxfield
> >>> <myles.maxfield at gmail.com> wrote:
> >>> > 1. The spec defines a grammar for the attributes. They're in
> uppercase.
> >>> > 2. Yes - 1.3 is the first version that lists DiffTime as an instance
> of
> >>> > RealFrac (so I can use the 'floor' function to pull out the number of
> >>> > seconds to render it)
> >>> > 3. I'll see what I can do.
> >>> >
> >>> > --Myles
> >>> >
> >>> >
> >>> > On Sat, Feb 4, 2012 at 9:06 PM, Michael Snoyman <michael at snoyman.com
> >
> >>> > wrote:
> >>> >>
> >>> >> Looks good, a few questions/requests:
> >>> >>
> >>> >> 1. Is there a reason to upper-case all the attributes?
> >>> >> 2. Is the time >= 1.3 a requirements? Because that can cause a lot
> of
> >>> >> trouble for people.
> >>> >> 3. Can you send the patch as a Github pull request? It's easier to
> >>> >> track that way.
> >>> >>
> >>> >> Michael
> >>> >>
> >>> >> On Sat, Feb 4, 2012 at 1:21 AM, Myles C. Maxfield
> >>> >> <myles.maxfield at gmail.com> wrote:
> >>> >> > Here is the patch to Web.Cookie. I didn't modify the tests at all
> >>> >> > because
> >>> >> > they were already broken - they looked like they hadn't been
> updated
> >>> >> > since
> >>> >> > SetCookie only had 5 parameters. I did verify by hand that the
> patch
> >>> >> > works,
> >>> >> > though.
> >>> >> >
> >>> >> > Thanks,
> >>> >> > Myles
> >>> >> >
> >>> >> >
> >>> >> > On Thu, Feb 2, 2012 at 11:26 PM, Myles C. Maxfield
> >>> >> > <myles.maxfield at gmail.com> wrote:
> >>> >> >>
> >>> >> >> Alright, I'll make a small patch that adds 2 fields to SetCookie:
> >>> >> >> setCookieMaxAge :: Maybe DiffTime
> >>> >> >> setCookieSecureOnly :: Bool
> >>> >> >>
> >>> >> >> I've also gotten started on those cookie functions. I'm currently
> >>> >> >> writing
> >>> >> >> tests for them.
> >>> >> >>
> >>> >> >> @Chris: The best advice I can give is that Chrome (what I'm using
> >>> >> >> as a
> >>> >> >> source on all this) has the data baked into a .cc file. However,
> >>> >> >> they
> >>> >> >> have
> >>> >> >> directions in a README and a script which will parse the list and
> >>> >> >> generate
> >>> >> >> that source file. I recommend doing this. That way, the Haskell
> >>> >> >> module
> >>> >> >> would
> >>> >> >> have 2 source files: one file that reads the list and generates
> the
> >>> >> >> second
> >>> >> >> file, which is a very large source file that contains each
> element
> >>> >> >> in
> >>> >> >> the
> >>> >> >> list. The list should export `elem`-type queries. I'm not quite
> >>> >> >> sure
> >>> >> >> how to
> >>> >> >> handle wildcards that appear in the list - that part is up to
> you.
> >>> >> >> Thanks
> >>> >> >> for helping out with this :]
> >>> >> >>
> >>> >> >> --Myles
> >>> >> >>
> >>> >> >>
> >>> >> >> On Thu, Feb 2, 2012 at 10:53 PM, Michael Snoyman
> >>> >> >> <michael at snoyman.com>
> >>> >> >> wrote:
> >>> >> >>>
> >>> >> >>> Looks good to me too. I agree with Aristid: let's make the
> change
> >>> >> >>> to
> >>> >> >>> cookie itself. Do you want to send a pull request? I'm also
> >>> >> >>> considering making the SetCookie constructor hidden like we have
> >>> >> >>> for
> >>> >> >>> Request, so that if in the future we realize we need to add some
> >>> >> >>> other
> >>> >> >>> settings, it doesn't break the API.
> >>> >> >>>
> >>> >> >>> Chris: I would recommend compiling it into the module. Best bet
> >>> >> >>> would
> >>> >> >>> likely being converting the source file to Haskell source.
> >>> >> >>>
> >>> >> >>> Michael
> >>> >> >>>
> >>> >> >>> On Fri, Feb 3, 2012 at 6:32 AM, Myles C. Maxfield
> >>> >> >>> <myles.maxfield at gmail.com> wrote:
> >>> >> >>> > Alright. After reading the spec, I have these questions /
> >>> >> >>> > concerns:
> >>> >> >>> >
> >>> >> >>> > The spec supports the "Max-Age" cookie attribute, which
> >>> >> >>> > Web.Cookies
> >>> >> >>> > doesn't.
> >>> >> >>> >
> >>> >> >>> > I see two possible solutions to this. The first is to have
> >>> >> >>> > parseSetCookie
> >>> >> >>> > take a UTCTime as an argument which will represent the current
> >>> >> >>> > time
> >>> >> >>> > so
> >>> >> >>> > it
> >>> >> >>> > can populate the setCookieExpires field by adding the Max-Age
> >>> >> >>> > attribute
> >>> >> >>> > to
> >>> >> >>> > the current time. Alternatively, that function can return an
> IO
> >>> >> >>> > SetCookie so
> >>> >> >>> > it can ask for the current time by itself (which I think is
> >>> >> >>> > inferior
> >>> >> >>> > to
> >>> >> >>> > taking the current time as an argument). Note that the spec
> says
> >>> >> >>> > to
> >>> >> >>> > prefer
> >>> >> >>> > Max-Age over Expires.
> >>> >> >>> > Add a field to SetCookie of type Maybe DiffTime which
> represents
> >>> >> >>> > the
> >>> >> >>> > Max-Age
> >>> >> >>> > attribute
> >>> >> >>> >
> >>> >> >>> > Cookie code should be aware of the Public Suffix List as a
> part
> >>> >> >>> > of
> >>> >> >>> > its
> >>> >> >>> > domain verification. The cookie code only needs to be able to
> >>> >> >>> > tell
> >>> >> >>> > if a
> >>> >> >>> > specific string is in the list (W.Ascii -> Bool)
> >>> >> >>> >
> >>> >> >>> > I propose making an entirely unrelated package,
> >>> >> >>> > public-suffix-list,
> >>> >> >>> > with a
> >>> >> >>> > module Network.PublicSuffixList, which will expose this
> >>> >> >>> > function, as
> >>> >> >>> > well as
> >>> >> >>> > functions about parsing the list itself. Thoughts?
> >>> >> >>> >
> >>> >> >>> > Web.Cookie doesn't have a "secure-only" attribute. Adding one
> in
> >>> >> >>> > is
> >>> >> >>> > straightforward enough.
> >>> >> >>> > The spec describes cookies as a property of HTTP, not of the
> >>> >> >>> > World
> >>> >> >>> > Wide
> >>> >> >>> > Web.
> >>> >> >>> > Perhaps "Web.Cookie" should be renamed? Just a thought; it
> >>> >> >>> > doesn't
> >>> >> >>> > really
> >>> >> >>> > matter to me.
> >>> >> >>> >
> >>> >> >>> > As for Network.HTTP.Conduit.Cookie, the spec describes in
> >>> >> >>> > section
> >>> >> >>> > 5.3
> >>> >> >>> > "Storage Model" what fields a Cookie has. Here is my proposal
> >>> >> >>> > for
> >>> >> >>> > the
> >>> >> >>> > functions it will expose:
> >>> >> >>> >
> >>> >> >>> > receiveSetCookie :: SetCookie -> Req.Request m -> UTCTime ->
> >>> >> >>> > Bool ->
> >>> >> >>> > CookieJar -> CookieJar
> >>> >> >>> >
> >>> >> >>> > Runs the algorithm described in section 5.3 "Storage Model"
> >>> >> >>> > The UTCTime is the current-time, the Bool is whether or not
> the
> >>> >> >>> > caller
> >>> >> >>> > is an
> >>> >> >>> > HTTP-based API (as opposed to JavaScript or anything else)
> >>> >> >>> >
> >>> >> >>> > updateCookieJar :: Res.Response a -> Req.Request m -> UTCTime
> ->
> >>> >> >>> > CookieJar
> >>> >> >>> > -> (CookieJar, Res.Response a)
> >>> >> >>> >
> >>> >> >>> > Applies "receiveSetCookie" to a Response. The output CookieJar
> >>> >> >>> > is
> >>> >> >>> > stripped
> >>> >> >>> > of any Set-Cookie headers.
> >>> >> >>> > Specifies "True" for the Bool in receiveSetCookie
> >>> >> >>> >
> >>> >> >>> > computeCookieString :: Req.Request m -> CookieJar -> UTCTime
> ->
> >>> >> >>> > Bool
> >>> >> >>> > ->
> >>> >> >>> > (W.Ascii, CookieJar)
> >>> >> >>> >
> >>> >> >>> > Runs the algorithm described in section 5.4 "The Cookie
> Header"
> >>> >> >>> > The UTCTime and Bool are the same as in receiveSetCookie
> >>> >> >>> >
> >>> >> >>> > insertCookiesIntoRequest :: Req.Request m -> CookieJar ->
> >>> >> >>> > UTCTime ->
> >>> >> >>> > (Req.Request m, CookieJar)
> >>> >> >>> >
> >>> >> >>> > Applies "computeCookieString" to a Request. The output cookie
> >>> >> >>> > jar
> >>> >> >>> > has
> >>> >> >>> > updated last-accessed-times.
> >>> >> >>> > Specifies "True" for the Bool in computeCookieString
> >>> >> >>> >
> >>> >> >>> > evictExpiredCookies :: CookieJar -> UTCTime -> CookieJar
> >>> >> >>> >
> >>> >> >>> > Runs the algorithm described in the last part of section 5.3
> >>> >> >>> > "Storage
> >>> >> >>> > Model"
> >>> >> >>> >
> >>> >> >>> > This will make the relevant part of 'http' look like:
> >>> >> >>> >
> >>> >> >>> >     go count req'' cookie_jar'' = do
> >>> >> >>> >         now <- liftIO $ getCurrentTime
> >>> >> >>> >         let (req', cookie_jar') = insertCookiesIntoRequest
> req''
> >>> >> >>> > (evictExpiredCookies cookie_jar'' now) now
> >>> >> >>> >         res' <- httpRaw req' manager
> >>> >> >>> >         let (cookie_jar, res) = updateCookieJar res' req' now
> >>> >> >>> > cookie_jar'
> >>> >> >>> >         case getRedirectedRequest req' (responseHeaders res)
> >>> >> >>> > (W.statusCode
> >>> >> >>> > (statusCode res)) of
> >>> >> >>> >             Just req -> go (count - 1) req cookie_jar
> >>> >> >>> >             Nothing -> return res
> >>> >> >>> >
> >>> >> >>> > I plan to not allow for a user-supplied cookieFilter function.
> >>> >> >>> > If
> >>> >> >>> > they
> >>> >> >>> > want
> >>> >> >>> > that functionality, they can re-implement the
> >>> >> >>> > redirection-following
> >>> >> >>> > logic.
> >>> >> >>> >
> >>> >> >>> > Any thoughts on any of this?
> >>> >> >>> >
> >>> >> >>> > Thanks,
> >>> >> >>> > Myles
> >>> >> >>> >
> >>> >> >>> > On Wed, Feb 1, 2012 at 5:19 PM, Myles C. Maxfield
> >>> >> >>> > <myles.maxfield at gmail.com>
> >>> >> >>> > wrote:
> >>> >> >>> >>
> >>> >> >>> >> Nope. I'm not. The RFC is very explicit about how to handle
> >>> >> >>> >> cookies.
> >>> >> >>> >> As
> >>> >> >>> >> soon as I'm finished making sense of it (in terms of Haskell)
> >>> >> >>> >> I'll
> >>> >> >>> >> send
> >>> >> >>> >> another proposal email.
> >>> >> >>> >>
> >>> >> >>> >> On Feb 1, 2012 3:25 AM, "Michael Snoyman" <
> michael at snoyman.com>
> >>> >> >>> >> wrote:
> >>> >> >>> >>>
> >>> >> >>> >>> You mean you're *not* making this proposal?
> >>> >> >>> >>>
> >>> >> >>> >>> On Wed, Feb 1, 2012 at 7:30 AM, Myles C. Maxfield
> >>> >> >>> >>> <myles.maxfield at gmail.com> wrote:
> >>> >> >>> >>> > Well, this is embarrassing. Please disregard my previous
> >>> >> >>> >>> > email.
> >>> >> >>> >>> > I
> >>> >> >>> >>> > should
> >>> >> >>> >>> > learn to read the RFC *before* submitting proposals.
> >>> >> >>> >>> >
> >>> >> >>> >>> > --Myles
> >>> >> >>> >>> >
> >>> >> >>> >>> >
> >>> >> >>> >>> > On Tue, Jan 31, 2012 at 6:37 PM, Myles C. Maxfield
> >>> >> >>> >>> > <myles.maxfield at gmail.com> wrote:
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> Here are my initial ideas about supporting cookies. Note
> >>> >> >>> >>> >> that
> >>> >> >>> >>> >> I'm
> >>> >> >>> >>> >> using
> >>> >> >>> >>> >> Chrome for ideas since it's open source.
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> Network/HTTP/Conduit/Cookies.hs file
> >>> >> >>> >>> >> Exporting the following symbols:
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> type StuffedCookie = SetCookie
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> A regular SetCookie can have Nothing for its Domain and
> >>> >> >>> >>> >> Path
> >>> >> >>> >>> >> attributes. A
> >>> >> >>> >>> >> StuffedCookie has to have these fields set.
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> type CookieJar = [StuffedCookie]
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> Chrome's cookie jar is implemented as (the C++ equivalent
> >>> >> >>> >>> >> of)
> >>> >> >>> >>> >> Map
> >>> >> >>> >>> >> W.Ascii
> >>> >> >>> >>> >> StuffedCookie. The key is the "eTLD+1" of the domain, so
> >>> >> >>> >>> >> lookups
> >>> >> >>> >>> >> for
> >>> >> >>> >>> >> all
> >>> >> >>> >>> >> cookies for a given domain are fast.
> >>> >> >>> >>> >> I think I'll stay with just a list of StuffedCookies just
> >>> >> >>> >>> >> to
> >>> >> >>> >>> >> keep
> >>> >> >>> >>> >> it
> >>> >> >>> >>> >> simple. Perhaps a later revision can implement the faster
> >>> >> >>> >>> >> map.
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> getRelevantCookies :: Request m -> CookieJar -> UTCTime
> ->
> >>> >> >>> >>> >> (CookieJar,
> >>> >> >>> >>> >> Cookies)
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> Gets all the cookies from the cookie jar that should be
> set
> >>> >> >>> >>> >> for
> >>> >> >>> >>> >> the
> >>> >> >>> >>> >> given
> >>> >> >>> >>> >> Request.
> >>> >> >>> >>> >> The time argument is whatever "now" is (it's pulled out
> of
> >>> >> >>> >>> >> the
> >>> >> >>> >>> >> function so
> >>> >> >>> >>> >> the function can remain pure and easily testable)
> >>> >> >>> >>> >> The function will also remove expired cookies from the
> >>> >> >>> >>> >> cookie
> >>> >> >>> >>> >> jar
> >>> >> >>> >>> >> (given
> >>> >> >>> >>> >> what "now" is) and return the filtered cookie jar
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> putRelevantCookies :: Request m -> CookieJar ->
> >>> >> >>> >>> >> [StuffedCookie]
> >>> >> >>> >>> >> ->
> >>> >> >>> >>> >> CookieJar
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> Insert cookies from a server response into the cookie
> jar.
> >>> >> >>> >>> >> The first argument is only used for checking to see which
> >>> >> >>> >>> >> cookies
> >>> >> >>> >>> >> are
> >>> >> >>> >>> >> valid (which cookies match the requested domain, etc, so
> >>> >> >>> >>> >> site1.com
> >>> >> >>> >>> >> can't set
> >>> >> >>> >>> >> a cookie for site2.com)
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> stuffCookie :: Request m -> SetCookie -> StuffedCookie
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> If the SetCookie's fields are Nothing, fill them in given
> >>> >> >>> >>> >> the
> >>> >> >>> >>> >> Request
> >>> >> >>> >>> >> from
> >>> >> >>> >>> >> which it originated
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> getCookies :: Response a -> ([SetCookie], Response a)
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> Pull cookies out of a server response. Return the
> response
> >>> >> >>> >>> >> with
> >>> >> >>> >>> >> the
> >>> >> >>> >>> >> Set-Cookie headers filtered out
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> putCookies :: Request a -> Cookies -> Request a
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> A wrapper around renderCookies. Inserts some cookies
> into a
> >>> >> >>> >>> >> request.
> >>> >> >>> >>> >> Doesn't overwrite cookies that are already set in the
> >>> >> >>> >>> >> request
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> These functions will be exported from
> Network.HTTP.Conduit
> >>> >> >>> >>> >> as
> >>> >> >>> >>> >> well, so
> >>> >> >>> >>> >> callers can use them to re-implement redirection chains
> >>> >> >>> >>> >> I won't implement a cookie filtering function (like what
> >>> >> >>> >>> >> Network.Browser
> >>> >> >>> >>> >> has)
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> If you want to have arbitrary handling of cookies,
> >>> >> >>> >>> >> re-implement
> >>> >> >>> >>> >> redirection following. It's not very difficult if you use
> >>> >> >>> >>> >> the
> >>> >> >>> >>> >> API
> >>> >> >>> >>> >> provided,
> >>> >> >>> >>> >> and the 'http' function is open source so you can use
> that
> >>> >> >>> >>> >> as a
> >>> >> >>> >>> >> reference.
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> I will implement the functions according to RFC 6265
> >>> >> >>> >>> >> I will also need to write the following functions. Should
> >>> >> >>> >>> >> they
> >>> >> >>> >>> >> also be
> >>> >> >>> >>> >> exported?
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> canonicalizeDomain :: W.Ascii -> W.Ascii
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> turns "..a.b.c..d.com..." to "a.b.c.d.com"
> >>> >> >>> >>> >> Technically necessary for domain matching (Chrome does
> it)
> >>> >> >>> >>> >> Perhaps unnecessary for a first pass? Perhaps we can
> trust
> >>> >> >>> >>> >> users
> >>> >> >>> >>> >> for
> >>> >> >>> >>> >> now?
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> domainMatches :: W.Ascii -> W.Ascii -> Maybe W.Ascii
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> Does the first domain match against the second domain?
> >>> >> >>> >>> >> If so, return the prefix of the first that isn't in the
> >>> >> >>> >>> >> second
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> pathMatches :: W.Ascii -> W.Ascii -> Bool
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> Do the paths match?
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> In order to implement domain matching, I have to have
> >>> >> >>> >>> >> knowledge
> >>> >> >>> >>> >> of
> >>> >> >>> >>> >> the Public Suffix List so I know that
> >>> >> >>> >>> >> sub1.sub2.pvt.k12.wy.us
> >>> >> >>> >>> >> can
> >>> >> >>> >>> >> set
> >>> >> >>> >>> >> a
> >>> >> >>> >>> >> cookie for sub2.pvt.k12.wy.us but not for k12.wy.us
> >>> >> >>> >>> >> (because
> >>> >> >>> >>> >> pvt.k12.wy.us
> >>> >> >>> >>> >> is a "suffix"). There are a variety of ways to implement
> >>> >> >>> >>> >> this.
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> As far as I can tell, Chrome does it by using a script
> >>> >> >>> >>> >> (which a
> >>> >> >>> >>> >> human
> >>> >> >>> >>> >> periodically runs) which parses the list at creates a .cc
> >>> >> >>> >>> >> file
> >>> >> >>> >>> >> that is
> >>> >> >>> >>> >> included in the build.
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> I might be wrong about the execution of the script; it
> >>> >> >>> >>> >> might be
> >>> >> >>> >>> >> a
> >>> >> >>> >>> >> build
> >>> >> >>> >>> >> step. If it is a build step, however, it is suspicious
> that
> >>> >> >>> >>> >> a
> >>> >> >>> >>> >> build
> >>> >> >>> >>> >> target
> >>> >> >>> >>> >> would try to download a file...
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> Any more elegant ideas?
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> Feedback on any/all of the above would be very helpful
> >>> >> >>> >>> >> before I
> >>> >> >>> >>> >> go
> >>> >> >>> >>> >> off
> >>> >> >>> >>> >> into the weeds on this project.
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> Thanks,
> >>> >> >>> >>> >> Myles C. Maxfield
> >>> >> >>> >>> >>
> >>> >> >>> >>> >> On Sat, Jan 28, 2012 at 8:17 PM, Michael Snoyman
> >>> >> >>> >>> >> <michael at snoyman.com>
> >>> >> >>> >>> >> wrote:
> >>> >> >>> >>> >>>
> >>> >> >>> >>> >>> Thanks, looks great! I've merged it into the Github
> tree.
> >>> >> >>> >>> >>>
> >>> >> >>> >>> >>> On Sat, Jan 28, 2012 at 8:36 PM, Myles C. Maxfield
> >>> >> >>> >>> >>> <myles.maxfield at gmail.com> wrote:
> >>> >> >>> >>> >>> > Ah, yes, you're completely right. I completely agree
> >>> >> >>> >>> >>> > that
> >>> >> >>> >>> >>> > moving
> >>> >> >>> >>> >>> > the
> >>> >> >>> >>> >>> > function into the Maybe monad increases readability.
> >>> >> >>> >>> >>> > This
> >>> >> >>> >>> >>> > kind
> >>> >> >>> >>> >>> > of
> >>> >> >>> >>> >>> > function
> >>> >> >>> >>> >>> > is what the Maybe monad was designed for.
> >>> >> >>> >>> >>> >
> >>> >> >>> >>> >>> > Here is a revised patch.
> >>> >> >>> >>> >>> >
> >>> >> >>> >>> >>> >
> >>> >> >>> >>> >>> > On Sat, Jan 28, 2012 at 8:28 AM, Michael Snoyman
> >>> >> >>> >>> >>> > <michael at snoyman.com>
> >>> >> >>> >>> >>> > wrote:
> >>> >> >>> >>> >>> >>
> >>> >> >>> >>> >>> >> On Sat, Jan 28, 2012 at 1:20 AM, Myles C. Maxfield
> >>> >> >>> >>> >>> >> <myles.maxfield at gmail.com> wrote:
> >>> >> >>> >>> >>> >> > the fromJust should never fail, beceause of the
> guard
> >>> >> >>> >>> >>> >> > statement:
> >>> >> >>> >>> >>> >> >
> >>> >> >>> >>> >>> >> >     | 300 <= code && code < 400 && isJust l'' &&
> >>> >> >>> >>> >>> >> > isJust
> >>> >> >>> >>> >>> >> > l' =
> >>> >> >>> >>> >>> >> > Just $
> >>> >> >>> >>> >>> >> > req
> >>> >> >>> >>> >>> >> >
> >>> >> >>> >>> >>> >> > Because of the order of the && operators, it will
> >>> >> >>> >>> >>> >> > only
> >>> >> >>> >>> >>> >> > evaluate
> >>> >> >>> >>> >>> >> > fromJust
> >>> >> >>> >>> >>> >> > after it makes sure that the argument isJust. That
> >>> >> >>> >>> >>> >> > function
> >>> >> >>> >>> >>> >> > in
> >>> >> >>> >>> >>> >> > particular
> >>> >> >>> >>> >>> >> > shouldn't throw any exceptions - it should only
> >>> >> >>> >>> >>> >> > return
> >>> >> >>> >>> >>> >> > Nothing.
> >>> >> >>> >>> >>> >> >
> >>> >> >>> >>> >>> >> > Knowing that, I don't quite think I understand what
> >>> >> >>> >>> >>> >> > your
> >>> >> >>> >>> >>> >> > concern
> >>> >> >>> >>> >>> >> > is.
> >>> >> >>> >>> >>> >> > Can
> >>> >> >>> >>> >>> >> > you
> >>> >> >>> >>> >>> >> > elaborate?
> >>> >> >>> >>> >>> >>
> >>> >> >>> >>> >>> >> You're right, but I had to squint really hard to
> prove
> >>> >> >>> >>> >>> >> to
> >>> >> >>> >>> >>> >> myself
> >>> >> >>> >>> >>> >> that
> >>> >> >>> >>> >>> >> you're right. That's the kind of code that could
> easily
> >>> >> >>> >>> >>> >> be
> >>> >> >>> >>> >>> >> broken
> >>> >> >>> >>> >>> >> in
> >>> >> >>> >>> >>> >> future updates by an unwitting maintainer (e.g., me).
> >>> >> >>> >>> >>> >> To
> >>> >> >>> >>> >>> >> protect
> >>> >> >>> >>> >>> >> the
> >>> >> >>> >>> >>> >> world from me, I'd prefer if the code didn't have the
> >>> >> >>> >>> >>> >> fromJust.
> >>> >> >>> >>> >>> >> This
> >>> >> >>> >>> >>> >> might be a good place to leverage the Monad instance
> of
> >>> >> >>> >>> >>> >> Maybe.
> >>> >> >>> >>> >>> >>
> >>> >> >>> >>> >>> >> Michael
> >>> >> >>> >>> >>> >
> >>> >> >>> >>> >>> >
> >>> >> >>> >>> >>
> >>> >> >>> >>> >>
> >>> >> >>> >>> >
> >>> >> >>> >
> >>> >> >>> >
> >>> >> >>
> >>> >> >>
> >>> >> >
> >>> >
> >>> >
> >>
> >>
> >>
> >> _______________________________________________
> >> Haskell-Cafe mailing list
> >> Haskell-Cafe at haskell.org
> >> http://www.haskell.org/mailman/listinfo/haskell-cafe
> >>
> >
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20120207/107b0737/attachment.htm>