#<p>
# Demonstration of the exception package
#</p>
#<p>
# <b>Author:</b> Steve Wampler (<i>sbw@tapestry.tucson.az.us</i>)
#</p>
#<p>
#  This file is in the <i>public domain</i>.
#</p>
#<p>
#  Demonstration of exception handling.
#  A call with any numeric argument other than three runs without Exception.
#  Any non-numeric argument throws a NumException (locally defined) while
#  a call with the argument 3 throws an Exception (base class for
#  all Exceptions).
#</p>
#<p>
#  The result of calling:
#<pre>
#    ExceptionDemo 1 2 3 4 a 6
#</pre>
#  is:
#<pre>
#    x is '1'.
#    x is '2'.
#    Exception: bad value of 3:
#        g [ExceptionDemo.icn:96]
#        f [ExceptionDemo.icn:80]
#        main [ExceptionDemo.icn:56]
#    
#    x is '4'.
#    NumException: 'a' is not a number:
#        g [ExceptionDemo.icn:93]
#        f [ExceptionDemo.icn:80]
#        main [ExceptionDemo.icn:56]
#    
#    x is '6'.
#</pre>
#<p>

import exception

#<p>
#  A simple example of subclassing the base Exception class.
#</p>
class NumException : Exception()
    method getMessage()
        return "NumException: " || (\message | "unknown")
    end
end

procedure main(args)

    every i := !args do {

        case Try().call{ f(i) } of {   # note use of PDCO!

            Try().catch("NumException"): {
                    Try().showException()
                    }

            Try().catch(): {    # catches all other exceptions
                    # Here's an alternative approach to handling
                    #   an exception (does same as above, in this demo):
                    x := Try().getException()
                    write(&errout, x.getMessage(), ":\n", x.getLocation())
                    }

            }

        }
        
end

#<p>
#  Simple function that outputs the result of another function.
#    Used to show that exception handling is a true 'throw'.
#  <[param i - arbitrary value]>
#</p>
procedure f(i)
    write("x is '",g(i),"'.")
end

#<p>
#  Simple function that performs (meaningless) work but can
#    throw two different types of Exceptions.
# <[param i - arbitrary value]>
# <[returns i if <tt>numeric(i) ~= 3</tt>]>
# <[Throws NumException if argument is <i>not</i> numeric]>
# <[Throws Exception if argument is <tt><b>3</b></tt>]>
#</p>
procedure g(i)
    if not numeric(i) then {
       NumException().throw("'"||i||"' is not a number")
       }
    if i = 3 then {
       Exception().throw("bad value of "||i)
       }
    return i
end