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Remove impossible case in generic instance #40

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Remove impossible case in generic instance #40

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Remove impossible case in generic instance
treeowl Jun 9, 2022
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treeowl Jun 9, 2022
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28 changes: 12 additions & 16 deletions lib/Fmt/Internal/Generic.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -108,22 +108,18 @@ instance (GetFields a, Constructor c) => GBuildable (M1 C c a) where
-- * Ordinarily e.g. "Foo" is prefix and e.g. ":|" is infix
-- * However, "Foo" can be infix when defined as "a `Foo` b"
-- * And ":|" can be prefix when defined as "(:|) a b"
gbuild c@(M1 x) = case conFixity c of
Infix _ _
| [a, b] <- fields -> format "({} {} {})" a infixName b
-- this case should never happen, but still
| otherwise -> format "<{}: {}>"
prefixName
(mconcat (intersperse ", " fields))
Prefix
| isTuple -> tupleF fields
| conIsRecord c -> nameF (build prefixName) (blockMapF fieldsWithNames)
| null (getFields x) -> build prefixName
-- I believe that there will be only one field in this case
| null (conName c) -> mconcat (intersperse ", " fields)
| otherwise -> format "<{}: {}>"
prefixName
(mconcat (intersperse ", " fields))
gbuild c@(M1 x)
| Infix _ _ <- conFixity c
-- There will always be two fields in this context.
, [a, b] <- fields = format "({} {} {})" a infixName b
| isTuple = tupleF fields
| conIsRecord c = nameF (build prefixName) (blockMapF fieldsWithNames)
| null (getFields x) = build prefixName
-- I believe that there will be only one field in this case
| null (conName c) = mconcat (intersperse ", " fields)
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@treeowl treeowl Jun 9, 2022

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How can the conName ever be null? Was this just a mistake?

| otherwise = format "<{}: {}>"
prefixName
(mconcat (intersperse ", " fields))
where
(prefixName, infixName)
| ":" `isPrefixOf` conName c = ("(" ++ conName c ++ ")", conName c)
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