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#97, make sure OneofSubfield generates well-typed code for non-Maybe #99

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Apr 17, 2019
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#97, make sure OneofSubfield generates well-typed code for non-Maybe #99

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15 changes: 8 additions & 7 deletions src/Proto3/Suite/DotProto/Generate.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -868,17 +868,18 @@ messageInstD ctxt parentIdent msgIdent messageParts = do
-- Constructor y -> encodeMessageField num (Nested (Just y)) -- for embedded messages
-- Constructor y -> encodeMessageField num (ForceEmit y) -- for everything else
let mkAlt (OneofSubfield fieldNum conName _ dpType options) = do
let wrapMaybe
let isMaybe
| Prim (Named tyName) <- dpType
, Just DotProtoKindMessage <- dotProtoTypeInfoKind <$> M.lookup tyName ctxt
= HsParen . HsApp (HsVar (haskellName "Just"))
= Just DotProtoKindMessage == fmap dotProtoTypeInfoKind (M.lookup tyName ctxt)
| otherwise
= forceEmitE
= False

xE <- wrapE ctxt options dpType
. wrapMaybe
$ HsVar (unqual_ "y")
let wrapJust = HsParen . HsApp (HsVar (haskellName "Just"))

xE <- (if isMaybe then id else fmap forceEmitE)
. wrapE ctxt options dpType
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Using dimap would be nice here.

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Sorry, I don't see how to use dimap at all. Any hints?

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@themattchan themattchan Apr 17, 2019 •
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Oops, you're right -- I thought both the pre- and post- operations were enabled by isMaybe.

This might read better though:

let adapt | isMaybe = lmap wrapJust
          | otherwise = rmap (fmap forceEmitE)

xE <- adapt (wrapE ctxt options dpType) (HsVar (unqual_ "y"))

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I find that harder to read. I guess I'd usually (. wrapJust) and (fmap forceEmitE .) rather than lmap/rmap - and in this case I'm not sure it's clearer at all. But happy to go that way if you want.

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I was thinking that it would be better to consolidate the adjustments predicated on isMaybe, but on second thought the extra indirection obfuscates matters.

. (if isMaybe then wrapJust else id)
$ HsVar (unqual_ "y")

pure $ alt_ (HsPApp (unqual_ conName) [patVar "y"])
(HsUnGuardedAlt (apply encodeMessageFieldE [fieldNumberE fieldNum, xE]))
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