MFP compat: s/fail/error/ in compileStmt - #19
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csabahruska
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Jul 3, 2019
| fs@(FunAlt n vs _: _) -> case groupBy ((==) `on` fst) [(length vs, n) | FunAlt n vs _ <- fs] of | ||
| [gs@((num, _): _)] | ||
| | num == 0 && length gs > 1 -> fail $ "redefined " ++ sName n ++ ":\n" ++ show (vcat $ pShow . sourceInfo . snd <$> gs) | ||
| | num == 0 && length gs > 1 -> error $ "redefined " ++ sName n ++ ":\n" ++ show (vcat $ pShow . sourceInfo . snd <$> gs) |
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Does not this change the semantics?
The error is more lazy than fail AFAIK.
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Disclaimer: I'm far from an expert in Haskell (I have a few hobby projects written in it)…
I think if I understood the MonadFail Proposal correctly, fail for Monads that didn't have a "reasonable" fail implementation and will not become MonadFail in the new proposal, was already implemented by calling error (which is part of why they are removing fail for those Monads).
If someone who actually is familiar with the internals of the MFP could confirm this, that would be good to know for sure.
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This gets rid of one of the issues on GHC 8.8.