https://wiki.haskell.org/index.php?title=Error&feed=atom&action=history
Error - Revision history
2024-03-28T13:48:29Z
Revision history for this page on the wiki
MediaWiki 1.35.5
https://wiki.haskell.org/index.php?title=Error&diff=65249&oldid=prev
Ennm: Clarified a bit
2022-08-07T15:56:52Z
<p>Clarified a bit</p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td>
<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 15:56, 7 August 2022</td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>An '''error''' denotes a programming error.</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>An '''error''' denotes a programming error.</div></td>
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<td class="diff-marker">−</td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The Prelude function <hask>error</hask> represents an error with a message,</div></td>
<td class="diff-marker">+</td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The Prelude function <hask>error</hask> represents an error with a<ins class="diffchange diffchange-inline"> custom</ins> message,</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><hask>undefined</hask> represents an error with a standard message.</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><hask>undefined</hask> represents an error with a standard message.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>For a Haskell program, an <hask>undefined</hask> value cannot be distinguished from an infinite loop,</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>For a Haskell program, an <hask>undefined</hask> value cannot be distinguished from an infinite loop,</div></td>
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Ennm
https://wiki.haskell.org/index.php?title=Error&diff=40862&oldid=prev
Christian: removed line break
2011-07-08T10:01:25Z
<p>removed line break</p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 10:01, 8 July 2011</td>
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<td colspan="2" class="diff-lineno">Line 5:</td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>e.g. <hask>let x=x+1 in x :: Int</hask>. Almost not.</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>e.g. <hask>let x=x+1 in x :: Int</hask>. Almost not.</div></td>
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<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>So ''error'' and ''[[Bottom|undefined value]]'' are somehow synonyms in Haskell.</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>So ''error'' and ''[[Bottom|undefined value]]'' are somehow synonyms in Haskell.</div></td>
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<td class="diff-marker">−</td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Since Haskell is [[non-strict semantics|non-strict]],</div></td>
<td class="diff-marker">+</td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Since Haskell is [[non-strict semantics|non-strict]],<ins class="diffchange diffchange-inline"> the occurence of an error within an expression is not necessarily an error, if the erroneous value is ignored somewhere, e.g. <hask> False && undefined </hask>.</ins></div></td>
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<td class="diff-marker">−</td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>the occurence of an error within an expression is not necessarily an error, if the erroneous value is ignored somewhere, e.g. <hask> False && undefined </hask>.</div></td>
<td colspan="2" class="diff-empty"> </td>
</tr>
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<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>However, if an expression finally evaluates to bottom or hangs in an infinite loop, then this is definitely a programming error.</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>However, if an expression finally evaluates to bottom or hangs in an infinite loop, then this is definitely a programming error.</div></td>
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<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Consider for instance <hask> fromJust x </hask> or</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Consider for instance <hask> fromJust x </hask> or</div></td>
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Christian
https://wiki.haskell.org/index.php?title=Error&diff=40861&oldid=prev
Christian: removed line break
2011-07-08T10:00:06Z
<p>removed line break</p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 10:00, 8 July 2011</td>
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<td colspan="2" class="diff-lineno">Line 6:</td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>So ''error'' and ''[[Bottom|undefined value]]'' are somehow synonyms in Haskell.</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>So ''error'' and ''[[Bottom|undefined value]]'' are somehow synonyms in Haskell.</div></td>
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<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Since Haskell is [[non-strict semantics|non-strict]],</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Since Haskell is [[non-strict semantics|non-strict]],</div></td>
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<td class="diff-marker">−</td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>the occurence of an error within an expression is not necessarily an error,</div></td>
<td class="diff-marker">+</td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>the occurence of an error within an expression is not necessarily an error,<ins class="diffchange diffchange-inline"> if the erroneous value is ignored somewhere, e.g. <hask> False && undefined </hask>.</ins></div></td>
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<td class="diff-marker">−</td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>if the erroneous value is ignored somewhere, e.g. <hask> False && undefined </hask>.</div></td>
<td colspan="2" class="diff-empty"> </td>
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<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>However, if an expression finally evaluates to bottom or hangs in an infinite loop, then this is definitely a programming error.</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>However, if an expression finally evaluates to bottom or hangs in an infinite loop, then this is definitely a programming error.</div></td>
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<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Consider for instance <hask> fromJust x </hask> or</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Consider for instance <hask> fromJust x </hask> or</div></td>
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Christian
https://wiki.haskell.org/index.php?title=Error&diff=32171&oldid=prev
Lemming: link to Error vs. Exception
2009-12-05T22:33:39Z
<p>link to Error vs. Exception</p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 22:33, 5 December 2009</td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* [[Exception]]</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* [[Exception]]</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* [[Error vs. Exception]]</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[Category:Glossary]]</div></td>
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Lemming
https://wiki.haskell.org/index.php?title=Error&diff=17236&oldid=prev
Lemming: bottom
2007-12-08T16:35:39Z
<p>bottom</p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 16:35, 8 December 2007</td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>For a Haskell program, an <hask>undefined</hask> value cannot be distinguished from an infinite loop,</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>For a Haskell program, an <hask>undefined</hask> value cannot be distinguished from an infinite loop,</div></td>
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<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>e.g. <hask>let x=x+1 in x :: Int</hask>. Almost not.</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>e.g. <hask>let x=x+1 in x :: Int</hask>. Almost not.</div></td>
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<td class="diff-marker">−</td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>So ''error'' and ''undefined value'' are somehow synonyms in Haskell.</div></td>
<td class="diff-marker">+</td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>So ''error'' and ''<ins class="diffchange diffchange-inline">[[Bottom|</ins>undefined value<ins class="diffchange diffchange-inline">]]</ins>'' are somehow synonyms in Haskell.</div></td>
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<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Since Haskell is [[non-strict semantics|non-strict]],</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Since Haskell is [[non-strict semantics|non-strict]],</div></td>
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<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>the occurence of an error within an expression is not necessarily an error,</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>the occurence of an error within an expression is not necessarily an error,</div></td>
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Lemming
https://wiki.haskell.org/index.php?title=Error&diff=17228&oldid=prev
Lemming: explanation
2007-12-07T21:26:53Z
<p>explanation</p>
<p><b>New page</b></p><div>An '''error''' denotes a programming error.<br />
The Prelude function <hask>error</hask> represents an error with a message,<br />
<hask>undefined</hask> represents an error with a standard message.<br />
For a Haskell program, an <hask>undefined</hask> value cannot be distinguished from an infinite loop,<br />
e.g. <hask>let x=x+1 in x :: Int</hask>. Almost not.<br />
So ''error'' and ''undefined value'' are somehow synonyms in Haskell.<br />
Since Haskell is [[non-strict semantics|non-strict]],<br />
the occurence of an error within an expression is not necessarily an error,<br />
if the erroneous value is ignored somewhere, e.g. <hask> False && undefined </hask>.<br />
However, if an expression finally evaluates to bottom or hangs in an infinite loop, then this is definitely a programming error.<br />
Consider for instance <hask> fromJust x </hask> or<br />
better <hask> fromMaybe (error "I know for sure, that x is Just, because ...") x </hask>.<br />
If the user sees according errors, then something is wrong which only the programmer can repair.<br />
These are really errors by the programmer and cannot be the final result in a correct program.<br />
Thus there is (almost) no way to recover from an error, at least no recommended one.<br />
<br />
However, you might have programmed a server which shall also keep running,<br />
if some service crashes due to a programming error.<br />
Or you want to quit a buggy program with a message like:<br />
"The impossible happened, a program error occured. Please send an e-mail with the following stack trace to the developer."<br />
The possibility to catch such errors in the <hask>IO</hask> monad is really tempting for abuse.<br />
So please think twice before you want to catch (and hide) an error,<br />
whether the thing you want to handle is actually an [[exception]].<br />
<br />
<br />
== See also ==<br />
<br />
* [[Exception]]<br />
<br />
[[Category:Glossary]]</div>
Lemming