Re: Exception Handling

[rav@goanna.cs.rmit.edu.au (Robin Vowels)]

	"Marin David Condic, 407.796.8997, M/S 731-93" <condicma@PWFL.COM> writes:

	>Felix Kasza <felixk@MAILBAG.SHD.DE> writes:
	>>I don't know -- but I do know that IBM's /360 architecture uses a
	>>mechanism for OS calls which looks very much like a trap.  PDPs used
	>>similar features to handle illegal memory references.  In the late 60s
	>>or early 70s, I saw an APL interpreter for the PDP that expressly made
	>>use of this although it didn't export the functionality to the
	>>programmer (APL has no concept of an exception).
	>>
	>    Well, if we include "hardware" in the picture, you'd have to go
	>    back to the very first invention of an interrupt. Assemblers, of
	>    course, let you write an interrupt handler and in that sense had
	>    "exception processing."

	>    When did it get incorporated in computer languages? That requires
	>    an answer to the question: "What exactly do you mean by 'exception
	>    processing'?" "Asynchronous transfer of control when an error is
	>    detected by the hardware or the programmer" would allow any
	>    language which gave you the ability to write an interrupt service
	>    routine and/or write a software triggered interrupt to qualify.
	>    That's most of them - except since this was always hardware
	>    dependent, it was probably not done as part of any "language
	>    standard" (more likely a vendor supplied utility).

	>    If we mean "programmer triggered exceptions" then we'd have to
	>    look to all the languages which provided some kind of syntax
	>    similar to: "ON ERROR THEN GOTO XXXX" - which would include quite
	>    a few very antiquated languages.

	>    If we mean "language triggered exceptions" (runtime checks
	>    inserted by the language translator and unseen by the programmer
	>    which may or may not include various hardware interrupts or
	>    exceptions which transfer control to a programmer specified chunk
	>    of code) then I *think* that Ada83 pretty much invented it.

Certainly one of the earliest -- if not *the* earliest -- was
PL/I, which in 1966 introduced exception handling for a wide
range of machine and programmer-defined exceptions.

OTOMH, they included 
   fixed-point overflow, floating-point overflow, floating-point
underflow, subscriptrange (for subscript errors), stringrange
(for substring errors), division by zero, size, endpage (for
handling end-of-page exceptions), endfile (for end-of-file),
data conversion errors, various file exceptions,
as well as the programmer-defined exceptions.  There was also
a facility for handling errors of a general nature (ERROR),
and even one for handling the end-of-job (FINISH).

   For data conversion errors, built-in functions enabled
access to the erroneous data fields, and corresponding
pseudo variables enabled the erroneous data to be
replaced with legitimate data, and the conversion re-attempted
if reqquired.

   These facilities are still in PL/I, and -- of course --
have been enhanced over the years.

	>    I am
	>    reasonably fluent in Fortran, Cobol, Pascal, C, and Ada and I have
	>    a passing knowlege of a number of more obscure languages like
	>    Lisp, Snobol, RPG, etc., and Ada was the first language I've ever
	>    encountered which included something in its syntax which meets
	>    this definition.