StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
primarykey
Id
7111890
data
AcceptedAnswerId
0
AnswerCount
0
ClosedDate
CommentCount
0
CommunityOwnedDate
CreationDate
2011-08-18T17:56:40.300
FavoriteCount
0
LastActivityDate
2011-08-18T18:05:42.370
LastEditDate
2011-08-18T18:05:42.370
LastEditorUserId
204932
OwnerUserId
204932
ParentId
7111522
PostTypeId
2
Score
7
ViewCount
0
LastEditorDisplayName
text
Body
<p>Here's a pseudocodey sketch of how you might use the <a href="http://hackage.haskell.org/packages/archive/mtl/2.0.1.0/doc/html/Control-Monad-State-Lazy.html"><code>State</code></a> monad to thread the search state through the computation:</p> <pre><code>import Control.Monad.State type SearchState = ... type Move = ... type Fitness = ... determineMoves :: State SearchState [Move] determineMoves = do -- since determineMoves is in the State monad, we can grab the state here st <- get ... evaluateMoves :: [Move] -> [(Move, Fitness)] evaluateMoves = ... chooseMove :: [(Move, Fitness)] -> Move chooseMove = ... -- makeMove is not itself monadic, but operates on the SearchState -- type we're threading through with the State monad makeMove :: Move -> SearchState -> SearchState makeMove m st = ... loop :: State SearchState () loop = do moves <- determineMoves let candidates = evaluateMoves moves move = chooseMove candidates -- we pass a function (SearchState -> SearchState) to modify in -- order to update the threaded SearchState modify (makeMove move) loop </code></pre> <p>Notice that even though your main computation is in the state monad, not every component has to be in the monad. Here, <code>evaluateMoves</code> and <code>chooseMove</code> are non-monadic, and I've used <code>let</code> to show you how to explicitly integrate them into a <code>do</code> block. Once you get comfortable with this style, though, you'll probably want to get comfortable using <code><$></code> (aka <code>fmap</code>) and function composition to get more succinct:</p> <pre><code>loop :: State SearchState () loop = do move <- (chooseMove . evaluateMoves) <$> determineMoves modify (makeMove move) loop </code></pre>
Tags
Title
singulars
PostAcceptedAnswerId
1. This table or related slice is empty.
PostParentId
1. POWhen to use Haskell monads
  singulars
  PostTypePostTypeId
  PTQuestion
PostTypePostTypeId
1. PTAnswer
UserLastEditorUserId
1. USacfoltzer
UserOwnerUserId
1. USacfoltzer
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. VO
  singulars
  PostPostId
  PO
  UserUserId
  This table or related slice is empty.
  VoteTypeVoteTypeId
  VTUpMod
2. VO
  singulars
  PostPostId
  PO
  UserUserId
  This table or related slice is empty.
  VoteTypeVoteTypeId
  VTUpMod
3. VO
  singulars
  PostPostId
  PO
  UserUserId
  This table or related slice is empty.
  VoteTypeVoteTypeId
  VTUpMod
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.