Steve Wampler wrote:
...
For a while, I thought about trying to implement an exception handling
mechanism using co-expressions, but just never had the heart to dive in.
This got me thinking about it again, so I've implemented a simple
Exception handling mechanism for Unicon. (It's missing the ability
to produce a stack trace because I don't have my Unicon book at home
and couldn't figure out how to do so without it! Suggested fixes
are *welcome*.) I think this is a pretty interesting use of
co-expressions.
I haven't tested it much - in fact, the simple program that follows is
the *only* test I've run! There are two basic classes:
Exception: the object that represents the exception
Try: the mechanism that implements the exception handling (really
a catch/throw mechanism). A robust version of this could be
embedded directly in Unicon and given a cleaner syntax :)
Both of these are found in the Exceptions package at:
http://tapestry.tucson.az.us/unicon
(they are built on other classes in the above library, but could be
implemented on top of Rob Parlatt's work just as easily...)
Here's a simple example of the use (this is the ExceptionTest
sample program also found at the above site):
import Exceptions
#<p>
# A simple example of subclassing the base Exception class.
#</p>
class NumException : Exception()
end
#<p>
# Test of Exception handling.
# A numeric argument <> three runs without Exception.
# A non-numeric argument throws NumException while
# a call with the argument 3 throws an Exception (base class for
# all Exceptions).
#</p>
procedure main(args)
i := get(args) | 0
case x := Try().call{ f(i) } of { # Note that call is a PDCO!
Try().isException(x, "NumException"):
write("NumException: ",x.getMessage(),": ",
x.getLocation())
Try().isException(x):
write(x.getMessage(),": ",x.getLocation())
default: write("x is '",x,"'.")
}
end
#<p>
# Simple function that performs (meaningless) work but can
# throw two different types of Exceptions.
#</p>
procedure f(i)
if numeric(i) = 3 then {
Exception().throw("bad value of "||i)
}
else if not numeric(i) then {
NumException().throw("'"||i||"'")
}
return i
end
I hope someone finds this interesting.
Steve
--
Steve Wampler [EMAIL PROTECTED]
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