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From: gmt@CS.ARIZONA.EDU ("Gregg Townsend")
Newsgroups: comp.lang.icon
Subject: Re:  Uses of dynamic typing
Message-ID: <9011170450.AA03673@owl.cs.arizona.edu>
Date: 17 Nov 90 04:50:18 GMT
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I've used Icon's type flexibility a few times to implement traps in
subroutine packages.  The paradigm works like this:

(1)  call enable() passing an arbitrary procedure p and other object x
     along with whatever is necessary to specify the trap conditions.

(2)  when the trap condition occurs -- for example, on every 60th
     call to an output routine -- p(x) is called using p and x
     from the enable() call.  Because x can be any type including
     a list or record, any desired amount of data can be passed to p.

This is clumsier in C because instead of an arbitrary object x one must
pass a *pointer* to x, with an appropriate cast, and then access the data
indirectly.

To pick a nit, printf actually can be written in standard C, because the
format specifies the expected types of the remaining arguments and there
are standard routines for retrieving them.  There are other problems such
as a danger that getc() has been replaced, but they're irrelevant to this
discussion.

    Gregg Townsend / Computer Science Dept / Univ of Arizona / Tucson, AZ 85721
    +1 602 621 4325     gmt@cs.arizona.edu     110 57 16 W / 32 13 45 N / +758m