Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>The <a href="http://hackage.haskell.org/package/control-monad-exception">Control.Monad.Exception</a> library allows strongly typed exceptions to be used in non IO code. This allows functions to throw errors, and easily compose with functions that throw different errors. For example:</p> <pre><code>{-# LANGUAGE RankNTypes, MultiParamTypeClasses, FunctionalDependencies #-} {-# LANGUAGE FlexibleInstances #-} import Prelude hiding (catch) import Control.Monad.Exception data FooException = FooException deriving (Show, Typeable) instance Exception FooException data BarErrors = BarErrors deriving (Show, Typeable) instance Exception BarErrors data BazErrors = BazErrors deriving (Show, Typeable) instance Exception BazErrors -- sample functions foo :: (Throws FooException l) =&gt; a -&gt; EM l a foo a = return a bar :: (Throws BarErrors l) =&gt; a -&gt; EM l a bar _ = throw BarErrors baz :: (Throws BazErrors l) =&gt; a -&gt; EM l a baz a = return a -- using all at once: allAtOnce :: (Throws FooException l, Throws BarErrors l, Throws BazErrors l) =&gt; a -&gt; EM l String allAtOnce x = do _ &lt;- foo x _ &lt;- bar x _ &lt;- baz x return "success!" -- now running the code, catching the exceptions: run :: a -&gt; String run x = runEM $ allAtOnce x `catch` (\(_ :: FooException) -&gt; return "foo failed") `catch` (\BarErrors -&gt; return "bar failed") `catch` (\BazErrors -&gt; return "baz failed") -- run 3 results in "bar failed" </code></pre> <p>See also the papers <a href="http://users.dsic.upv.es/~jiborra/papers/explicitexceptions.pdf">Explicitly Typed Exceptions for Haskell</a> and <a href="http://community.haskell.org/~simonmar/papers/ext-exceptions.pdf">An Extensible Dynamically-Typed Hierarchy of Exceptions</a> for more details on using this library.</p>
    singulars
    1. This table or related slice is empty.
    1. POExpressive and composable error types
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USDavid Miani
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POExpressive and composable error types
      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. COBrilliant, thanks!
      singulars
      1. PO
      1. USjberryman
    2. COAfter doing some research, what I think will suit my library is to define my library's functions polymorphically in the `Failure` class from the 'failure' package, here: http://hackage.haskell.org/package/failure . That lets me express the kinds of exceptions that can be raised in the type sig, and gives my users the option of using something simple like `Maybe`, or something more robust like control-monad-exception (which provides an instance). Thanks again.
      singulars
      1. PO
      1. USjberryman
 

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