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Proofreading (#3)

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@ggreif thanks for proofreading!
This commit is contained in:
Gabor Greif 2019-01-26 11:20:29 +01:00 committed by Marcin Szamotulski
parent 4ce35b64d8
commit 2cdbb82c09
1 changed files with 9 additions and 8 deletions
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17
examples/src/LoginStateMachine.hs
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@ -53,12 +53,14 @@ data State a (st :: StateType) where
runLoggedOut :: State a 'LoggedOutType -> Maybe a
runLoggedOut (LoggedOut a) = a
-- | Graph of transitions in the state machine. In abstract representation the
-- states do not show up, the only way to record some data is to addit to the
-- transition. Thus @'Logout'@ can carry data. When interpreted in a some
-- states do not show up, the only way to record some data is to add it to the
-- transition. Thus @'Logout'@ can carry data. When interpreted in some
-- category (e.g. @'Kleisli' m@) then the data will be avalable on
-- @'LoggedOut{} :: 'State' a st@.
--
data Tr a from to where
Login :: SStateType to -> Tr a (State a 'LoggedOutType) (State a to)
Logout :: Maybe a -> Tr a (State a 'LoggedInType) (State a 'LoggedOutType)
@ -168,9 +170,8 @@ accessSecret n HandleLogin{handleLogin} = lift $ do
-- | Get data following the protocol defined by the state machine.
--
-- Note: in GHC-8.6 we'd need @'MonadFail'@ constraint which prevents from
-- running this in @'Identity'@ monad. To avoid this we use @'runLoggedOut'@
-- function.
-- Note: in GHC-8.6.1 we'd need @'MonadFail'@ which prevents from running this in
-- @'Identity'@ monad. To avoid this we use the @'runLoggedOut'@ function.
getData
:: forall m a . Monad m
=> (forall x y. Tr a x y -> Kleisli m x y)
@ -183,15 +184,15 @@ getData nat n handleLogin = case foldNatLift nat (accessSecret n handleLogin) of
return ma
-- * Interpreters
-- To write an interpret it is enough to supply a natural transformation from
-- To write an interpreter it is enough to supply a natural transformation from
-- @'Tr' a from to@ to @'Kleisli' m@ for some monad @m@.
-- | A pure natural transformation from @'Tr'@ to @'Kleisli' m@ for some
-- @'Monad' m@. Note, that even though @'Kleisli'@ category seems redundant
-- here, as we don't use the monad in the transformation, we need
-- a transformation into a category that satisfies the @'Lifing'@ constraint.
-- This is bause we will need the monad whn @'foldNatLift'@ will walk over the
-- constructors of '@FreeEffCat'@ category.
-- This is because we will need the monad whn @'foldNatLift'@ will walk over the
-- constructors of the '@FreeLifting'@ category.
--
natPure :: forall m a from to. Monad m => Tr a from to -> Kleisli m from to
natPure = liftKleisli . nat