module Distribution.Solver.Types.Progress
    ( Progress(..)
    , foldProgress
    ) where

import Prelude ()
import Distribution.Solver.Compat.Prelude hiding (fail)

-- | A type to represent the unfolding of an expensive long running
-- calculation that may fail. We may get intermediate steps before the final
-- result which may be used to indicate progress and\/or logging messages.
--
data Progress step fail done = Step step (Progress step fail done)
                             | Fail fail
                             | Done done

-- This Functor instance works around a bug in GHC 7.6.3.
-- See https://gitlab.haskell.org/ghc/ghc/-/issues/7436#note_66637.
-- The derived functor instance caused a space leak in the solver.
instance Functor (Progress step fail) where
  fmap :: (a -> b) -> Progress step fail a -> Progress step fail b
fmap a -> b
f (Step step
s Progress step fail a
p) = step -> Progress step fail b -> Progress step fail b
forall step fail done.
step -> Progress step fail done -> Progress step fail done
Step step
s ((a -> b) -> Progress step fail a -> Progress step fail b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap a -> b
f Progress step fail a
p)
  fmap a -> b
_ (Fail fail
x)   = fail -> Progress step fail b
forall step fail done. fail -> Progress step fail done
Fail fail
x
  fmap a -> b
f (Done a
r)   = b -> Progress step fail b
forall step fail done. done -> Progress step fail done
Done (a -> b
f a
r)

-- | Consume a 'Progress' calculation. Much like 'foldr' for lists but with two
-- base cases, one for a final result and one for failure.
--
-- Eg to convert into a simple 'Either' result use:
--
-- > foldProgress (flip const) Left Right
--
foldProgress :: (step -> a -> a) -> (fail -> a) -> (done -> a)
             -> Progress step fail done -> a
foldProgress :: (step -> a -> a)
-> (fail -> a) -> (done -> a) -> Progress step fail done -> a
foldProgress step -> a -> a
step fail -> a
fail done -> a
done = Progress step fail done -> a
fold
  where fold :: Progress step fail done -> a
fold (Step step
s Progress step fail done
p) = step -> a -> a
step step
s (Progress step fail done -> a
fold Progress step fail done
p)
        fold (Fail fail
f)   = fail -> a
fail fail
f
        fold (Done done
r)   = done -> a
done done
r

instance Monad (Progress step fail) where
  return :: a -> Progress step fail a
return   = a -> Progress step fail a
forall (f :: * -> *) a. Applicative f => a -> f a
pure
  Progress step fail a
p >>= :: Progress step fail a
-> (a -> Progress step fail b) -> Progress step fail b
>>= a -> Progress step fail b
f  = (step -> Progress step fail b -> Progress step fail b)
-> (fail -> Progress step fail b)
-> (a -> Progress step fail b)
-> Progress step fail a
-> Progress step fail b
forall step a fail done.
(step -> a -> a)
-> (fail -> a) -> (done -> a) -> Progress step fail done -> a
foldProgress step -> Progress step fail b -> Progress step fail b
forall step fail done.
step -> Progress step fail done -> Progress step fail done
Step fail -> Progress step fail b
forall step fail done. fail -> Progress step fail done
Fail a -> Progress step fail b
f Progress step fail a
p

instance Applicative (Progress step fail) where
  pure :: a -> Progress step fail a
pure a
a  = a -> Progress step fail a
forall step fail done. done -> Progress step fail done
Done a
a
  Progress step fail (a -> b)
p <*> :: Progress step fail (a -> b)
-> Progress step fail a -> Progress step fail b
<*> Progress step fail a
x = (step -> Progress step fail b -> Progress step fail b)
-> (fail -> Progress step fail b)
-> ((a -> b) -> Progress step fail b)
-> Progress step fail (a -> b)
-> Progress step fail b
forall step a fail done.
(step -> a -> a)
-> (fail -> a) -> (done -> a) -> Progress step fail done -> a
foldProgress step -> Progress step fail b -> Progress step fail b
forall step fail done.
step -> Progress step fail done -> Progress step fail done
Step fail -> Progress step fail b
forall step fail done. fail -> Progress step fail done
Fail (((a -> b) -> Progress step fail a -> Progress step fail b)
-> Progress step fail a -> (a -> b) -> Progress step fail b
forall a b c. (a -> b -> c) -> b -> a -> c
flip (a -> b) -> Progress step fail a -> Progress step fail b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap Progress step fail a
x) Progress step fail (a -> b)
p

instance Monoid fail => Alternative (Progress step fail) where
  empty :: Progress step fail a
empty   = fail -> Progress step fail a
forall step fail done. fail -> Progress step fail done
Fail fail
forall a. Monoid a => a
mempty
  Progress step fail a
p <|> :: Progress step fail a
-> Progress step fail a -> Progress step fail a
<|> Progress step fail a
q = (step -> Progress step fail a -> Progress step fail a)
-> (fail -> Progress step fail a)
-> (a -> Progress step fail a)
-> Progress step fail a
-> Progress step fail a
forall step a fail done.
(step -> a -> a)
-> (fail -> a) -> (done -> a) -> Progress step fail done -> a
foldProgress step -> Progress step fail a -> Progress step fail a
forall step fail done.
step -> Progress step fail done -> Progress step fail done
Step (Progress step fail a -> fail -> Progress step fail a
forall a b. a -> b -> a
const Progress step fail a
q) a -> Progress step fail a
forall step fail done. done -> Progress step fail done
Done Progress step fail a
p