[Haskell-cafe] Contributing to http-conduit

[Michael Snoyman]

+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
>>> >> >>> >>> >>> >
>>> >> >>> >>> >>> >
>>> >> >>> >>> >>
>>> >> >>> >>> >>
>>> >> >>> >>> >
>>> >> >>> >
>>> >> >>> >
>>> >> >>
>>> >> >>
>>> >> >
>>> >
>>> >
>>
>>
>>
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