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chrisdone-artificial merged 4 commits into from
Oct 2, 2026
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Merged

Add support for exception handling #141

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f17fe50
Add `finally`, `onException`, `bracket` and `catch`
fpringle Oct 2, 2026
fac893d
Add `SomeException` and its `Show` instance
fpringle Oct 2, 2026
3e82386
Add examples for new functions
fpringle Oct 2, 2026
60e93b0
Update docs
fpringle Oct 2, 2026
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8 changes: 4 additions & 4 deletions docs/api/index.html
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37 changes: 37 additions & 0 deletions docs/examples/index.html
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Expand Up @@ -799,4 +799,41 @@ <h2>44-char.hell</h2><div class="sourceCode" id="cb1"><pre
class="sourceCode haskell"><code class="sourceCode haskell"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a>main <span class="ot">=</span> <span class="kw">do</span></span>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a> line <span class="ot">&lt;-</span> Text.getLine</span>
<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span><span class="fu">print</span> <span class="op">$</span> Text.all (<span class="dt">Eq</span><span class="op">.</span>eq <span class="ch">&#39;x&#39;</span>) line</span></code></pre></div>
<h2>45-enum.hell</h2><div class="sourceCode" id="cb1"><pre
class="sourceCode haskell"><code class="sourceCode haskell"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a>main <span class="ot">=</span> <span class="kw">do</span></span>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span><span class="fu">print</span> <span class="op">$</span> List.take <span class="dv">5</span> <span class="op">$</span> <span class="dt">Enum</span><span class="op">.</span><span class="fu">enumFrom</span> <span class="dv">1</span></span>
<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span><span class="fu">print</span> <span class="op">$</span> <span class="dt">Enum</span><span class="op">.</span><span class="fu">enumFromTo</span> <span class="dv">1</span> <span class="dv">10</span></span>
<span id="cb1-4"><a href="#cb1-4" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span><span class="fu">print</span> <span class="op">$</span> List.take <span class="dv">5</span> <span class="op">$</span> <span class="dt">Enum</span><span class="op">.</span><span class="fu">enumFrom</span> <span class="ch">&#39;a&#39;</span></span>
<span id="cb1-5"><a href="#cb1-5" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span><span class="fu">print</span> <span class="op">$</span> List.take <span class="dv">5</span> <span class="op">$</span> <span class="dt">Enum</span><span class="op">.</span><span class="fu">enumFrom</span> <span class="dt">Bool</span><span class="op">.</span><span class="dt">False</span></span>
<span id="cb1-6"><a href="#cb1-6" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span><span class="fu">print</span> <span class="op">$</span> List.take <span class="dv">5</span> <span class="op">$</span> <span class="dt">Enum</span><span class="op">.</span><span class="fu">enumFrom</span> (<span class="dt">Int</span><span class="op">.</span><span class="fu">toInteger</span> <span class="dv">1</span>)</span>
<span id="cb1-7"><a href="#cb1-7" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span><span class="fu">print</span> <span class="op">$</span> List.take <span class="dv">5</span> <span class="op">$</span> <span class="dt">Enum</span><span class="op">.</span><span class="fu">enumFrom</span> <span class="op">$</span></span>
<span id="cb1-8"><a href="#cb1-8" aria-hidden="true" tabindex="-1"></a> <span class="dt">Maybe</span><span class="op">.</span><span class="fu">maybe</span> (Error.error <span class="st">&quot;Bad day.&quot;</span>) Function.id <span class="op">$</span> Day.fromGregorianValid (<span class="dt">Int</span><span class="op">.</span><span class="fu">toInteger</span> <span class="dv">2020</span>) <span class="dv">01</span> <span class="dv">01</span></span>
<span id="cb1-9"><a href="#cb1-9" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-10"><a href="#cb1-10" aria-hidden="true" tabindex="-1"></a> <span class="co">-- simple list generators</span></span>
<span id="cb1-11"><a href="#cb1-11" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span><span class="fu">print</span> [<span class="dv">1</span> <span class="op">..</span> <span class="dv">3</span>]</span>
<span id="cb1-12"><a href="#cb1-12" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span><span class="fu">print</span> <span class="op">$</span> List.take <span class="dv">5</span> [<span class="ch">&#39;a&#39;</span> <span class="op">..</span>]</span></code></pre></div>
<h2>46-exceptions.hell</h2><div class="sourceCode" id="cb1"><pre
class="sourceCode haskell"><code class="sourceCode haskell"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a>main <span class="ot">=</span> <span class="kw">do</span></span>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span><span class="ot"> noSuchFile ::</span> <span class="dt">Text</span> <span class="ot">=</span> <span class="st">&quot;no/such/file.txt&quot;</span></span>
<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> printException <span class="ot">=</span> \e <span class="ot">-&gt;</span> <span class="kw">do</span> Text.hPutStr <span class="dt">IO</span><span class="op">.</span>stderr (<span class="dt">Show</span><span class="op">.</span><span class="fu">show</span> e <span class="op">&lt;&gt;</span> <span class="st">&quot;\n&quot;</span>)</span>
<span id="cb1-4"><a href="#cb1-4" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span><span class="fu">pure</span> <span class="st">&quot;&quot;</span></span>
<span id="cb1-5"><a href="#cb1-5" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> catchAndPrintException <span class="ot">=</span> \action <span class="ot">-&gt;</span> SomeException.catch action printException</span>
<span id="cb1-6"><a href="#cb1-6" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-7"><a href="#cb1-7" aria-hidden="true" tabindex="-1"></a> catchAndPrintException (Text.readFile noSuchFile)</span>
<span id="cb1-8"><a href="#cb1-8" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-9"><a href="#cb1-9" aria-hidden="true" tabindex="-1"></a> <span class="kw">let</span> file <span class="ot">=</span> <span class="st">&quot;file.txt&quot;</span></span>
<span id="cb1-10"><a href="#cb1-10" aria-hidden="true" tabindex="-1"></a> catchAndPrintException <span class="op">$</span></span>
<span id="cb1-11"><a href="#cb1-11" aria-hidden="true" tabindex="-1"></a> Exception.bracket</span>
<span id="cb1-12"><a href="#cb1-12" aria-hidden="true" tabindex="-1"></a> (<span class="dt">IO</span><span class="op">.</span>openFile file <span class="dt">IO</span><span class="op">.</span><span class="dt">ReadWriteMode</span>)</span>
<span id="cb1-13"><a href="#cb1-13" aria-hidden="true" tabindex="-1"></a> (\fileHandle <span class="ot">-&gt;</span> <span class="kw">do</span></span>
<span id="cb1-14"><a href="#cb1-14" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span>hClose fileHandle</span>
<span id="cb1-15"><a href="#cb1-15" aria-hidden="true" tabindex="-1"></a> Directory.removeFile file</span>
<span id="cb1-16"><a href="#cb1-16" aria-hidden="true" tabindex="-1"></a> )</span>
<span id="cb1-17"><a href="#cb1-17" aria-hidden="true" tabindex="-1"></a> (\fileHandle <span class="ot">-&gt;</span> <span class="kw">do</span></span>
<span id="cb1-18"><a href="#cb1-18" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span>hSetBuffering fileHandle <span class="dt">IO</span><span class="op">.</span><span class="dt">NoBuffering</span></span>
<span id="cb1-19"><a href="#cb1-19" aria-hidden="true" tabindex="-1"></a> Text.hPutStr fileHandle <span class="st">&quot;don&#39;t buffer me&quot;</span></span>
<span id="cb1-20"><a href="#cb1-20" aria-hidden="true" tabindex="-1"></a> Text.decodeUtf8 <span class="op">&lt;$&gt;</span> <span class="dt">ByteString</span><span class="op">.</span>hGet fileHandle <span class="dv">10</span></span>
<span id="cb1-21"><a href="#cb1-21" aria-hidden="true" tabindex="-1"></a> )</span>
<span id="cb1-22"><a href="#cb1-22" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-23"><a href="#cb1-23" aria-hidden="true" tabindex="-1"></a> <span class="dt">IO</span><span class="op">.</span><span class="fu">pure</span> ()</span></code></pre></div>
</html>
23 changes: 23 additions & 0 deletions examples/46-exceptions.hell
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@@ -0,0 +1,23 @@
main = do
let noSuchFile :: Text = "no/such/file.txt"
let printException = \e -> do Text.hPutStr IO.stderr (Show.show e <> "\n")
IO.pure ""
let catchAndPrintException = \action -> SomeException.catch action printException

catchAndPrintException (Text.readFile noSuchFile)

let file = "file.txt"
catchAndPrintException $
Exception.bracket
(IO.openFile file IO.ReadWriteMode)
(\fileHandle -> do
IO.hClose fileHandle
Directory.removeFile file
)
(\fileHandle -> do
IO.hSetBuffering fileHandle IO.NoBuffering
Text.hPutStr fileHandle "don't buffer me"
Text.decodeUtf8 <$> ByteString.hGet fileHandle 10
)

IO.pure ()
11 changes: 10 additions & 1 deletion src/Hell.hs
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Expand Up @@ -59,7 +59,8 @@ import Data.ByteString.Builder (Builder)
import qualified Data.ByteString.Builder as Builder
import Control.Applicative (Alternative (..), optional)
import qualified Control.Concurrent as Concurrent
import Control.Exception (evaluate)
import Control.Exception (evaluate, SomeException)
import qualified Control.Exception as Exception
import Control.Monad.Reader
import Control.Monad.State.Strict
import Criterion.Measurement
Expand Down Expand Up @@ -864,6 +865,7 @@ instances =
instance0 @Show @Builder,
instance0 @Show @ExitCode,
instance0 @Show @Value,
instance0 @Show @SomeException,
entail1 @Eq @CI,
entail1 @Eq @[],
entail1 @Eq @Set,
Expand Down Expand Up @@ -1730,6 +1732,7 @@ supportedTypeConstructors =
("TimeOfDay", SomeTypeRep $ typeRep @TimeOfDay),
("Builder", SomeTypeRep $ typeRep @Builder),
("CI", SomeTypeRep $ typeRep @CI),
("SomeException", SomeTypeRep $ typeRep @SomeException),
-- Internal, hidden types
("hell:Hell.NilL", SomeTypeRep $ typeRep @('NilL)),
("hell:Hell.ConsL", SomeTypeRep $ typeRep @('ConsL)),
Expand Down Expand Up @@ -2394,6 +2397,12 @@ polyLits =
"Argument.help" options_help :: forall a. Text -> Options.Mod Options.ArgumentFields a
"Options.progDesc" options_progDesc :: forall a. Text -> Options.InfoMod a
"Options.header" options_header :: forall a. Text -> Options.InfoMod a

-- Exceptions
"Exception.finally" Exception.finally :: forall a b. IO a -> IO b -> IO a
"Exception.onException" Exception.onException :: forall a b. IO a -> IO b -> IO a
"Exception.bracket" Exception.bracket :: forall a b c. IO a -> (a -> IO b) -> (a -> IO c) -> IO c
"SomeException.catch" Exception.catch :: forall a. IO a -> (SomeException -> IO a) -> IO a
|]
in toplevel
)
Expand Down