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<p>I might still be tempted to do:</p>
<div>
<div>data DsMessage =</div>
<div> ...</div>
<div> | DsLiftedTcRnMessage !TcRnMessage</div>
<div> -- ^ A diagnostic coming straight from the
Typecheck-renamer.</div>
<div><br>
</div>
<div>
<div>
<div>data TcRnMessage =</div>
<div> ...</div>
<div> | TcRnLiftedDsMessage !DsMessage</div>
<div> -- ^ A diagnostic coming straight from the Desugarer.</div>
<div><br>
</div>
tying them together with hs-boot. Yes, that means one can do
some silly `TcRnLiftedDsMessage . DsLiftedTcRnMessage .
TcRnLiftedDsMessage ...`, but that could even show up in a
render as "while desugaring a splice during type checking,
while typechecking during desguaring, ..." so arguably the
information the wrapping isn't purely superfluous.</div>
<div><br>
</div>
<div>I think this would pose no practical problem today, while
still "soft enforcing" the abstraction boundaries we want.</div>
<div><br>
</div>
</div>
</div>
<div class="moz-cite-prefix">On 3/31/21 3:45 AM, Alfredo Di Napoli
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAFqA6+U_8pw9GCmczcWD-D8Rvfi=Zb0NFBpDs_7tKdO+H4p3ow@mail.gmail.com">
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<div dir="ltr">
<div dir="ltr">Follow up:
<div><br>
</div>
<div>Argh! I have just seen that I have a bunch of test
failures related to my MR (which, needless to say, it's
still WIP).</div>
<div><br>
</div>
<div>For example:</div>
<div><br>
</div>
<div>
<div>run/T9140.run.stdout.normalised 2021-03-31
09:35:48.000000000 +0200</div>
<div>@@ -1,12 +1,4 @@</div>
<div> </div>
<div>-<interactive>:2:5:</div>
<div>- You can't mix polymorphic and unlifted bindings: a
= (# 1 #)</div>
<div>- Probable fix: add a type signature</div>
<div>-</div>
<div>-<interactive>:3:5:</div>
<div>- You can't mix polymorphic and unlifted bindings: a
= (# 1, 3 #)</div>
<div>- Probable fix: add a type signature</div>
<div>-</div>
</div>
<div><br>
</div>
<div>So it looks like some diagnostic is now not being
reported and, surprise surprise, this was emitted from the
DsM monad.</div>
<div><br>
</div>
<div>I have the suspect that indeed Richard was right (like he
always is :) ) -- when we go from a DsM to a TcM monad (See
`initDsTc`) for example, I think we also need to carry into
the new monad all the diagnostics we collected so far.</div>
<div><br>
</div>
<div>This implies indeed a mutual dependency (as Simon pointed
out, heh).</div>
<div><br>
</div>
<div><br>
</div>
<div>So I think my cunning plan of embedding is crumbling -- I
suspect we would end up with a type `TcRnDsMessage` which
captures the dependency. </div>
<div><br>
</div>
<div>Sorry for not seeing it sooner!</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
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<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, 31 Mar 2021 at 08:05,
Alfredo Di Napoli <<a
href="mailto:alfredo.dinapoli@gmail.com"
moz-do-not-send="true">alfredo.dinapoli@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">Morning all,
<div><br>
</div>
<div><b>Richard</b>: sorry! Unfortunately MR !4798
is the cornerstone of this refactoring work but
it's also gargantuan. Let's discuss a plan to
attack it, but fundamentally there is a critical
mass of changes that needs to happen atomically
or it wouldn't make much sense, and alas this
doesn't play in our favour when it comes to MR
size and ease of review. However, to quickly
reply to your remak: currently (for the sake of
the "minimum-viable-product") I am trying to
stabilise the external interfaces, by which I
mean giving functions their final type signature
while I do what's easiest to make things
typecheck. In this phase what I think is the
easiest is to wrap the majority of diagnostics
into the `xxUnknownxx` constructor, and change
them gradually later. A fair warning, though:
you say "<span
style="color:rgb(26,26,26);font-family:Arial;font-size:13px">I
would think that a DsMessage would later be
wrapped in an envelope." This might be true
for Ds messages (didn't actually invest any
brain cycles to check that) but in general we
have to turn a message into an envelope as
soon as we have a chance to do so, because we
need to grab the `SrcSpan` and the `DynFlags`
*at the point of creation* of the diagnostics.
Carrying around a message and make it bubble
up at some random point won't be a good plan
(even for Ds messages). Having said that, I
clearly have very little knowledge about this
area of GHC, so feel free to disagree :)</span></div>
<div><span
style="color:rgb(26,26,26);font-family:Arial;font-size:13px"><br>
</span></div>
<div><span
style="color:rgb(26,26,26);font-family:Arial;font-size:13px"><b>John</b>:
Although it's a bit hard to predict how well
this is going to evolve, my current embedding,
to refresh everyone's memory, is the
following:</span></div>
<div><span
style="color:rgb(26,26,26);font-family:Arial;font-size:13px"><br>
</span></div>
<div>
<p
style="margin:0px;font-stretch:normal;font-size:13px;line-height:normal;font-family:Arial;color:rgb(26,26,26)"><span>data
DsMessage =</span></p>
<p
style="margin:0px;font-stretch:normal;font-size:13px;line-height:normal;font-family:Arial;color:rgb(26,26,26)"><span>
DsUnknownMessage !DiagnosticMessage</span></p>
<p
style="margin:0px;font-stretch:normal;font-size:13px;line-height:normal;font-family:Arial;color:rgb(26,26,26)"><span>
-- ^ Stop-gap constructor to ease the
migration.</span></p>
<p
style="margin:0px;font-stretch:normal;font-size:13px;line-height:normal;font-family:Arial;color:rgb(26,26,26)"><span>
| DsLiftedTcRnMessage !TcRnMessage</span></p>
<p
style="margin:0px;font-stretch:normal;font-size:13px;line-height:normal;font-family:Arial;color:rgb(26,26,26)"><span>
-- ^ A diagnostic coming straight from the
Typecheck-renamer.</span></p>
<p
style="margin:0px;font-stretch:normal;font-size:13px;line-height:normal;font-family:Arial;color:rgb(26,26,26)"><span>
-- More messages added in the future, of
course</span></p>
<p
style="margin:0px;font-stretch:normal;font-size:13px;line-height:normal;font-family:Arial;color:rgb(26,26,26)"><span><br>
</span></p>
<p
style="margin:0px;font-stretch:normal;font-size:13px;line-height:normal;font-family:Arial;color:rgb(26,26,26)"><span>At
first I thought this was the wrong way
around, due to Simon's comment, but this
actually creates pleasant external
interfaces. To give you a bunch of examples
from MR !4798:</span></p>
<p
style="margin:0px;font-stretch:normal;font-size:13px;line-height:normal;font-family:Arial;color:rgb(26,26,26)"><span><br>
</span></p>
<p
style="margin:0px;font-stretch:normal;font-size:13px;line-height:normal;font-family:Arial;color:rgb(26,26,26)"><span></span></p>
<p
style="margin:0px;font-stretch:normal;font-size:13px;line-height:normal;font-family:Arial;color:rgb(26,26,26)">deSugar
:: HscEnv -> ModLocation -> TcGblEnv
-> IO (Messages DsMessage, Maybe ModGuts)</p>
</div>
<div>
<div>deSugarExpr :: HscEnv -> LHsExpr GhcTc
-> IO (Messages DsMessage, Maybe CoreExpr)</div>
</div>
<div><br>
</div>
<div>Note something interesting: the second
function actually calls `runTcInteractive`
inside the body, but thanks to the
`DsLiftedTcRnMessage` we can still expose to the
consumer an opaque `DsMessage` , which is what I
would expect to see from a function called
"deSugarExpr". Conversely, I would be puzzled to
find those functions returning a
`TcRnDsMessage`.</div>
<div><br>
</div>
<div><br>
</div>
<div>Having said all of that, I am not advocating
this design is "the best". I am sure we will
iterate on it. I am just reporting that even
this baseline seems to be decent from an API
perspective :)</div>
<div><br>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, 31 Mar 2021 at
05:45, John Ericson <a class="moz-txt-link-rfc2396E" href="mailto:john.ericson@obsidian.systems"><john.ericson@obsidian.systems></a>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
<div>
<p>Alfredo also replied to this pointing his embedding
plan. I also prefer that, because I really wish TH
didn't smear together the phases so much. Moreover, I
hope with</p>
<p> - GHC proposals <a
href="https://github.com/ghc-proposals/ghc-proposals/pull/412"
target="_blank" moz-do-not-send="true">https://github.com/ghc-proposals/ghc-proposals/pull/412</a>
/ <a
href="https://github.com/ghc-proposals/ghc-proposals/pull/243"
target="_blank" moz-do-not-send="true">https://github.com/ghc-proposals/ghc-proposals/pull/243</a></p>
<p> - The parallelism work currently be planned in
<a
href="https://gitlab.haskell.org/ghc/ghc/-/wikis/Plan-for-increased-parallelism-and-more-detailed-intermediate-output"
target="_blank" moz-do-not-send="true">https://gitlab.haskell.org/ghc/ghc/-/wikis/Plan-for-increased-parallelism-and-more-detailed-intermediate-output</a>
<br>
</p>
<p>we might actually have an opportunity/extra
motivation to do that. Splices and quotes will still
induce intricate inter-phase dependencies, but I hope
that could be mediated by the driver rather than just
baked into each phase.</p>
<p>(One final step would be the "stuck macros" technique
of <a
href="https://www.youtube.com/watch?v=nUvKoG_V_U0"
target="_blank" moz-do-not-send="true">https://www.youtube.com/watch?v=nUvKoG_V_U0</a>
/ <a href="https://github.com/gelisam/klister"
target="_blank" moz-do-not-send="true">https://github.com/gelisam/klister</a>,
where TH splices would be able to making "blocking
queries" of the the compiler in ways that induce more
of these fine-grained dependencies.)</p>
<p>Anyways, while we could also do a "RnTsDsError" and
split later, I hope Alfredo's alternative of embedding
won't be too much harder and prepare us for these
exciting areas of exploration.<br>
</p>
<p>John</p>
<div>On 3/30/21 10:14 AM, Richard Eisenberg wrote:<br>
</div>
<blockquote type="cite"> <br>
<div><br>
<blockquote type="cite">
<div>On Mar 30, 2021, at 4:57 AM, Alfredo Di
Napoli <<a
href="mailto:alfredo.dinapoli@gmail.com"
target="_blank" moz-do-not-send="true">alfredo.dinapoli@gmail.com</a>>
wrote:</div>
<br>
<div><span
style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none;float:none;display:inline">I'll
explore the idea of adding a second IORef.</span></div>
</blockquote>
</div>
<br>
<div>Renaming/type-checking is already mutually
recursive. (The renamer must call the type-checker
in order to rename -- that is, evaluate -- untyped
splices. I actually can't recall why the
type-checker needs to call the renamer.) So we will
have a TcRnError. Now we see that the desugarer ends
up mixed in, too. We could proceed how Alfredo
suggests, by adding a second IORef. Or we could just
make TcRnDsError (maybe renaming that).</div>
<div><br>
</div>
<div>What's the disadvantage? Clients will have to
potentially know about all the different error forms
with either approach (that is, using my combined
type or using multiple IORefs). The big advantage to
separating is maybe module dependencies? But my
guess is that the dependencies won't be an issue
here, due to the fact that these components are
already leaning on each other. Maybe the advantage
is just in having smaller types? Maybe.</div>
<div><br>
</div>
<div>I don't have a great sense as to what to do here,
but I would want a clear reason that e.g. the TcRn
monad would have two IORefs, while other monads will
work with GhcMessage (instead of a whole bunch of
IORefs).</div>
<div><br>
</div>
<div>Richard</div>
<br>
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