StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
primarykey
Id
11702411
data
AcceptedAnswerId
0
AnswerCount
0
ClosedDate
CommentCount
2
CommunityOwnedDate
2012-07-28T15:42:57.713
CreationDate
2012-07-28T15:42:57.713
FavoriteCount
0
LastActivityDate
2016-02-29T05:33:13.307
LastEditDate
2016-02-29T05:33:13.307
LastEditorUserId
2755648
OwnerUserId
132273
ParentId
2104446
PostTypeId
2
Score
46
ViewCount
0
LastEditorDisplayName
text
Body
There is a lot to say in answer to your question, however, since you asked, I will offer this "rule of thumb." If you are using <code>do</code>-notation and your generated values[1] are not used in the expressions that you are sequencing[2], then that code can transform to an Applicative style. Similarly, if you use one or more of the generated values in an expression that is sequenced, then you must use <code>Monad</code> and <code>Applicative</code> is not strong enough to achieve the same code. For example, let us look at the following code: <pre><code>do a <- e1 b <- e2 c <- e3 return (f a b c) </code></pre> We see that in none of the expressions to the right of <code><-</code> do any of the generated values (<code>a</code>, <code>b</code>, <code>c</code>) appear. Therefore, we can transform it to using Applicative code. Here is one possible transformation: <pre><code>f <$> e1 <*> e2 <*> e3 </code></pre> and another: <pre><code>liftA3 f e1 e2 e3 </code></pre> On the other hand, take this piece of code for example: <pre><code>do a <- e1 b <- e2 a c <- e3 return (f b c) </code></pre> This code cannot use <code>Applicative</code>[3] because the generated value <code>a</code> is used later in an expression in the comprehension. This must use <code>Monad</code> to get to its result -- attempt to factor it into <code>Applicative</code> to get a feel for why. There are some further interesting and useful details on this subject, however, I just intended to give you this rule of thumb whereby you can skim over a <code>do</code>-comprehension and determine pretty quickly if it can be factored into <code>Applicative</code> style code. [1] Those that appear to the left of <code><-</code>. [2] Expressions that appear to the right of <code><-</code>. [3] strictly speaking, parts of it could, by factoring out <code>e2 a</code>.
Tags
Title
singulars
PostAcceptedAnswerId
1. This table or related slice is empty.
PostParentId
1. POHow do you use Control.Applicative to write cleaner Haskell?
 singulars
 PostTypePostTypeId
 PTQuestion
PostTypePostTypeId
1. PTAnswer
UserLastEditorUserId
1. USsid-kap
UserOwnerUserId
1. USTony Morris
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. COYou can sometimes mix Monad and Applicative operators if you like the applicative style. Your second do block can be written `f <$> (e1 >>= e2) <*> e3`
 singulars
 PostPostId
 PO
 UserUserId
 USAndrewC

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.