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From: ralph@CS.ARIZONA.EDU ("Ralph Griswold")
Newsgroups: comp.lang.icon
Subject: Re:  generation of procedures
Message-ID: <9002071611.AA13262@megaron.cs.arizona.edu>
Date: 7 Feb 90 16:11:17 GMT
References: <9002071557.AA01397@zk.cray.com>
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The procedures are generated by !plist as you surmised.  The first one
is then applied to the argument list, resulting in a procedure call.
If that call fails, !plist is resumed to produce another procedure.

Think of a procedure call as

	e0(e1, e2, ..., en)

The order of evaluation is e0, e1, e2, ..., en.  If all succeed, the value of e0
is applied to the values of e1, e2, ..., en. If the resulting procedure call
fails, en, ..., e2, e1, e0 are resumed in that order (assuming they suspended).
If any produces a new result, evaluation starts to the right again. In the
case you cite, only e0 is a generator, so failure of the procedure call
causes e0 to produce another procedure, which is then applied to the
arguments.  If any of the procedure calls fails, the process stops, since
there is nothing to drive further generation.  The effect is to apply the
procedures in plist until one succeeds.

  Ralph Griswold / Dept of Computer Science / Univ of Arizona / Tucson, AZ 85721
  +1 602 621 6609   ralph@cs.arizona.edu  uunet!arizona!ralph