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||| Monads and Functors
module Prelude.Monad
import Builtins
import Prelude.Functor
import public Prelude.Applicative
import Prelude.Basics
import Prelude.Foldable
import IO
%access public export
infixl 1 >>=
interface Applicative m => Monad (m : Type -> Type) where
||| Also called `bind`.
(>>=) : m a -> ((result : a) -> m b) -> m b
||| Also called `flatten` or mu
join : m (m a) -> m a
-- default implementations
(>>=) x f = join (f <$> x)
join x = x >>= id
||| For compatibility with Haskell. Note that monads are **not** free to
||| define `return` and `pure` differently!
return : Monad m => a -> m a
return = pure
%fragile return "`return` is provided for those coming from Haskell. Please use `pure` instead, which is equivalent."
||| Similar to `foldl`, but uses a function wrapping its result in a `Monad`.
||| Consequently, the final value is wrapped in the same `Monad`.
foldlM : (Foldable t, Monad m) => (funcM: a -> b -> m a) -> (init: a) -> (input: t b) -> m a
foldlM fm a0 = foldl (\ma,b => ma >>= flip fm b) (pure a0)
-- Annoyingly, these need to be here, so that we can use them in other
-- Prelude modules other than the top level.
Functor (IO' ffi) where
map f io = io_bind io (\b => io_pure (f b))
Applicative (IO' ffi) where
pure x = io_pure x
f <*> a = io_bind f (\f' =>
io_bind a (\a' =>
io_pure (f' a')))
Monad (IO' ffi) where
b >>= k = io_bind b k
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