Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>First of all, that style is actually rather idiomatic. Since you're doing two things to two different values, there is some irreducible complexity; the actual pattern match does not introduce much on its own. Besides, I personally find the explicit style very readable most of the time.</p> <p>However, there is an alternative. <code>Control.Arrow</code> has a bunch of functions for working with tuples. Since the function arrow <code>-&gt;</code> is an <code>Arrow</code> as well, all these work for normal functions. </p> <p>So you could rewrite your second example using <code>(***)</code> to combine two functions to work over tuples. This operator has the following type:</p> <pre><code>(***) :: a b c -&gt; a b' c' -&gt; a (b, b') (c, c') </code></pre> <p>If we replace <code>a</code> with <code>-&gt;</code>, we get:</p> <pre><code>(***) :: (b -&gt; c) -&gt; (b' -&gt; c') -&gt; ((b, b') -&gt; (c, c')) </code></pre> <p>So you could combine <code>(+ x)</code> and <code>(- x)</code> into a single function with <code>(+ x) *** (- x)</code>. This would be equivalent to:</p> <pre><code>\ (a, b) -&gt; (a + x, b - x) </code></pre> <p>Then you could use it in your recursion. Unfortunately, the <code>-</code> operator is stupid and doesn't work in sections, so you would have to write it with a lambda:</p> <pre><code>(+ x) *** (\ a -&gt; a - x) $ go xs </code></pre> <p>You can obviously imagine using any other operator, all of which <em>aren't</em> quite as stupid :).</p> <p>Honestly, I think this version is less readable than the original. However, in other cases, the <code>***</code> version <em>can</em> be more readable, so it's useful to know about it. In particular, if you were passing <code>(+ x) *** (- x)</code> into a higher-order function instead of applying it immediately, I think the <code>***</code> version would be better than an explicit lambda.</p>
    singulars
    1. This table or related slice is empty.
    1. POAvoid pattern matching in recursion
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USTikhon Jelvis
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POAvoid pattern matching in recursion
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COMay replace your `a` lambda with `(+(-x))` or `(subtract x)` or exist some problem? thank you! :)
      singulars
      1. PO
      1. USjosejuan
    2. CO@josejuan: Yeah, you can do either of those as well. I'm not a big fan of any of the options :P.
      singulars
      1. PO
      1. USTikhon Jelvis
    3. COSo it's arrows. The thought crossed my mind. And you are right, its still unclear if its better than the original, but it answered my question the most directly and clearly, so I'm going to accept your answer.
      singulars
      1. PO
      1. USfirefrorefiddle
 

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.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload