Exceptions: Difference between revisions
Add page to "Flow control" category.
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[[Category:Flow control]]
This task is to give an example of an exception handling routine
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X.try
X.throw SillyError(‘egg’)
X.catch SillyError se
print(se.message)</syntaxhighlight>
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}</syntaxhighlight>
=={{header|
==={{header|BBC BASIC}}===
<syntaxhighlight lang="bbcbasic"> ON ERROR PROCerror(ERR, REPORT$) : END
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{
constructor new()
<= super new("MyException raised");
}</syntaxhighlight>
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<syntaxhighlight lang="elena">try
{
}
catch
{
// handle exceptions of type MyException and derived
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'''Catching any exception'''
<syntaxhighlight lang="elena">
{
foo.fail()
catch(Exception e)
{
// handle any type of exception
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Exceptions in langur are hashes guaranteed to contain certain fields, even if they're empty.
<syntaxhighlight lang="langur">
catch
if .e
# change result...
} else {
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} else {
# no exception
}
...▼
An else section on a catch is optional.
===
An exception variable may be specified, or you can simply use the implicit variable, which is _err.
<syntaxhighlight lang="langur">100 / 0
catch
# change result
123
# rethrow the exception
}</syntaxhighlight>▼
throw
}
<syntaxhighlight lang="langur">val .safediv =
.safediv(7, 7) # 1
.safediv(7, 0) # 0
</syntaxhighlight>
=={{header|Lasso}}==
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see 1/0
Catch
raise("Sorry we can't divide 1/0" + nl)
Done
</syntaxhighlight>
=={{header|RPL}}==
Basic RPL allows a conditional branching on error:
≪ '''IFERR''' '1/0' EVAL '''THEN'''
<span style="color:red">"Can't divide "</span> ROT →STR + <span style="color:red">" by "</span> + SWAP →STR + '''END'''
≫
=={{header|Ruby}}==
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An exception is thrown by the ''die'' keyword, which, if not caught, it terminates the program with an appropriate exit code.
<syntaxhighlight lang="ruby">try {
die "I'm dead!"
}
}
▲catch { |type, msg|
▲ say "msg: #{msg}"; # msg: I'm dead! at test.sf line 2.
▲};
say "I'm alive..."
die "Now I'm dead!"
say "Or am I?"
{{out}}
<pre>
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msg: I'm dead! at test.sf line 2.
I'm alive...
Now I'm dead! at test.sf line
</pre>
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Here's an example of all this.
<syntaxhighlight lang="
if (!(a is Num && a.isInteger) || !(b is Num && b.isInteger)) Fiber.abort("Invalid argument(s).")
if (b == 0) Fiber.abort("Division by zero error.")
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Caught Num does not implement 'badMethod()'.
</pre>
=={{header|XPL0}}==
XPL0 does not have the commands throw, try and catch; nor their equivalents.
By default, exceptions such as divide-by-zero cause a program to abort.
That behavior is called error trapping. Robust programs disable error
trapping by passing an integer bit array to a built-in Trap intrinsic
that selectively disables about a dozen error traps (by setting their
corresponding bits to 0). The traps are often all disabled by simply
passing 'false' when a section of code is about to do something that
might cause an exception, such as accessing a disk file that might not be
available. In this case the intrinsic GetErr is called, which returns a
value indicating which error occurred; and if an error is detected, the
program can take appropriate action without simply aborting.
Generally, aborting on errors is suitable during the debugging stage, but
often it's the worst alternative for an end user.
A related intrinsic, Restart, is useful if an error is detected in a
procedure nested many levels deep. Instead of returning the error
indication up through the many levels, it can be easier to restart the
program. A call to the Rerun intrinsic distinguishes a restart from a
normal start, and that can be used to properly handle the error.
<syntaxhighlight lang "XPL0">
real A;
[Trap(false);
A:= Sqrt(-42.);
if GetErr then
Text(0, "Square root of a negative value.
");
RlOut(0, A);
]</syntaxhighlight>
{{out}}
<pre>
Square root of a negative value.
NAN</pre>
=={{header|zkl}}==
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