StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
primarykey
Id
17986659
data
AcceptedAnswerId
0
AnswerCount
0
ClosedDate
CommentCount
0
CommunityOwnedDate
CreationDate
2013-08-01T06:28:35.767
FavoriteCount
0
LastActivityDate
2013-08-01T06:36:38.863
LastEditDate
2013-08-01T06:36:38.863
LastEditorUserId
1295154
OwnerUserId
1295154
ParentId
17522198
PostTypeId
2
Score
2
ViewCount
0
LastEditorDisplayName
text
Body
Principally, you might be able to write an implementation for primitive, but not for internal, since it imposes a certain structure for your monad, which is only satisfied by the internal implementations of the IO and ST monads. However, my impression is that the problem is with the Data.Vector.Mutable module, whose requirements are overly strict. To use for example an IO Vector in a monad m, you principally only need an embedding of IO into m (i.e. the primitive method) and not vice versa (i.e. the internal method). If this is correct, they should try to subdivide the PrimMonad class into an embedding part and an isomorphism part, for example as follows: <pre><code>-- | Class of primitive state-transformer monads class Monad m => PrimMonadEmbed m where -- | State token type type PrimState m -- | Execute a primitive operation primitive :: (State# (PrimState m) -> (# State# (PrimState m), a #)) -> m a class PrimMonadEmbed m => PrimMonad m where -- | Expose the internal structure of the monad internal :: m a -> State# (PrimState m) -> (# State# (PrimState m), a #) </code></pre> This might be okay in terms of backwards compatibility since no custom instances can exist in user code. Making the requirement less strict would also make their code usable with transformed versions of the IO monad like StateT Int IO etc. You might try two things: <ul> <li>implement a partial instance for PrimMonad which only implements the primitive method and makes internal throw an error, and see if you can use the vector library like that</li> <li>contact the authors of the vector library you are using and ask them if the above proposal is realistic...</li> </ul> By the way, the following implementation of primitive should work (compare the source of STT to understand what went wrong in your code): <pre><code>{-# LANGUAGE TypeFamilies #-} {-# LANGUAGE UnboxedTuples #-} module Test where import Control.Monad.Primitive import Control.Monad.ST.Trans import Control.Monad.ST.Trans.Internal instance Monad m => PrimMonad (STT s m) where type PrimState (STT s m) = s primitive f = STT (\s -> case (f s) of (# s', v #) -> return (STTRet s' v)) internal _ = error "no implementation of internal for STT" </code></pre>
Tags
Title
singulars
PostAcceptedAnswerId
1. This table or related slice is empty.
PostParentId
1. PODefining PrimMonad instance for STT? (ST Transformer)
 singulars
 PostTypePostTypeId
 PTQuestion
PostTypePostTypeId
1. PTAnswer
UserLastEditorUserId
1. USDominique Devriese
UserOwnerUserId
1. USDominique Devriese
plurals
PostLinksPostIdRelatedPostId
1. This table or related slice is empty.
PostLinksRelatedPostIdPostId
1. This table or related slice is empty.
PostsAcceptedAnswerId
1. This table or related slice is empty.
PostsParentIdCreationDate
1. This table or related slice is empty.
VotesPostIdCreationDate
1. This table or related slice is empty.
CommentsPostId
1. This table or related slice is empty.

Querying!

Guidance

A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.