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| author | Herbert Valerio Riedel <hvr@gnu.org> | 2016-01-01 01:45:08 +0100 |
|---|---|---|
| committer | Herbert Valerio Riedel <hvr@gnu.org> | 2016-01-01 01:55:16 +0100 |
| commit | dafeb51f266793a67e8ae18ae39a2e2e87943824 (patch) | |
| tree | f1ef3abd7fc655e6b8896a6841f0efd9a39a39fe /compiler/prelude | |
| parent | 8afeaad919dc67643b4eff14efafb48b59039b2b (diff) | |
| download | haskell-dafeb51f266793a67e8ae18ae39a2e2e87943824.tar.gz | |
Canonicalise `MonadPlus` instances
This refactoring exploits the fact that since AMP, in most cases,
`instance MonadPlus` can be automatically derived from the respective
`Alternative` instance. This is because `MonadPlus`'s default method
implementations are fully defined in terms of `Alternative(empty, (<>))`.
Diffstat (limited to 'compiler/prelude')
| -rw-r--r-- | compiler/prelude/PrelRules.hs | 10 |
1 files changed, 4 insertions, 6 deletions
diff --git a/compiler/prelude/PrelRules.hs b/compiler/prelude/PrelRules.hs index 2a174b13fc..13e271bc66 100644 --- a/compiler/prelude/PrelRules.hs +++ b/compiler/prelude/PrelRules.hs @@ -656,13 +656,11 @@ instance MonadFail.MonadFail RuleM where #endif instance Alternative RuleM where - empty = mzero - (<|>) = mplus + empty = RuleM $ \_ _ _ -> Nothing + RuleM f1 <|> RuleM f2 = RuleM $ \dflags iu args -> + f1 dflags iu args <|> f2 dflags iu args -instance MonadPlus RuleM where - mzero = RuleM $ \_ _ _ -> Nothing - mplus (RuleM f1) (RuleM f2) = RuleM $ \dflags iu args -> - f1 dflags iu args `mplus` f2 dflags iu args +instance MonadPlus RuleM instance HasDynFlags RuleM where getDynFlags = RuleM $ \dflags _ _ -> Just dflags |