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garyb wants to merge 3 commits into from
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Add MonadZero and MonadPlus #5

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324ac4e
Add MonadZero and MonadPlus
garyb May 19, 2014
7e6cf14
Add `guard`
garyb May 19, 2014
e78cb33
Update docs
garyb May 19, 2014
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11 changes: 11 additions & 0 deletions README.md
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Expand Up @@ -36,10 +36,21 @@

## Module Control.Monad

### Type Classes

class (MonadZero m) <= MonadPlus m where
mplus :: forall a. m a -> m a -> m a

class (Monad m) <= MonadZero m where
mzero :: forall a. m a


### Values

foldM :: forall m a b. (Monad m) => (a -> b -> m a) -> a -> [b] -> m a

guard :: forall m. (MonadPlus m) => Prim.Boolean -> m Unit

replicateM :: forall m a. (Monad m) => Prim.Number -> m a -> m [a]

unless :: forall m. (Monad m) => Prim.Boolean -> m { } -> m { }
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10 changes: 10 additions & 0 deletions src/Control/Monad.purs
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@@ -1,5 +1,11 @@
module Control.Monad where

class (Monad m) <= MonadZero m where
mzero :: forall a. m a

class (MonadZero m) <= MonadPlus m where
mplus :: forall a. m a -> m a -> m a

replicateM :: forall m a. (Monad m) => Number -> m a -> m [a]
replicateM 0 _ = return []
replicateM n m = do
Expand All @@ -11,6 +17,10 @@ foldM :: forall m a b. (Monad m) => (a -> b -> m a) -> a -> [b] -> m a
foldM _ a [] = return a
foldM f a (b:bs) = f a b >>= \a' -> foldM f a' bs

guard :: forall m. (MonadPlus m) => Boolean -> m Unit
guard true = return unit
guard false = mzero

when :: forall m. (Monad m) => Boolean -> m {} -> m {}
when true m = m
when false _ = return {}
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