Summary

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	File:     dif.icn

	Subject:  Procedure to check for differences

	Author:   Robert J. Alexander

	Date:     August 14, 1996

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   This file is in the public domain.

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	dif(stream, compare, eof, group)
		generates a sequence of differences between an	arbitrary
		number of input streams.  Each result is returned as a list
		of diff_recs, one for each input stream, with each diff_rec
		containing a list of items that differ and their position
		in the input stream.

  The diff_rec type is declared as:

		record diff_rec(pos,diffs)

  dif() fails if there are no differences, i.e. it produces an empty
  result sequence.

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  For example, if two input streams are:

	a b c d e f g h
	a b d e f i j

  the output sequence would be:

	[diff_rec(3,[c]),diff_rec(3,[])]
	[diff_rec(7,[g,h]),diff_rec(6,[i,j])

  The arguments to dif(stream,compare,eof,group) are:

	stream		A list of data objects that represent input streams
			from which dif will extract its input "records".
			The elements can be of several different types which
			result in different actions, as follows:

			   Type			   Action
			===========	=============================
			file		file is "read" to get records

			co-expression	co-expression is activated to
					get records

			list		records are "gotten" (get()) from
					the list

			diff_proc	a record type defined in "dif" to
					allow a procedure (or procedures)
					suppled by dif's caller to be called
					to get records.  Diff_proc has two
					fields, the procedure to call and the
					argument to call it with.  Its
					definition looks like this:

					   record diff_proc(proc,arg)
			

  Optional arguments:

	compare		Item comparison procedure -- succeeds if
			"equal", otherwise fails (default is the
			identity "===" comparison).  The comparison
			must allow for the fact that the eof object
			(see next) might be an argument, and a pair of
			eofs must compare equal.

	eof		An object that is distinguishable from other
			objects in the stream.  Default is &null.

	group		A procedure that is called with the current number
			of unmatched items as its argument.  It must
			return the number of matching items required
			for file synchronization to occur.  Default is
			the formula Trunc((2.0 * Log(M)) + 2.0) where
			M is the number of unmatched items.

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This file is part of the (main) package.

dif(stream, compare, eof, group)

diffread(f)

  diffread() -- Read a line from an input stream.

groupfactor(m)

  groupfactor() -- Determine how many like lines we need to close
  off a group of differences.  This is the default routine -- the
  caller may provide his own.

 Compute: Trunc((2.0 * Log(m)) + 2.0)

diff_file(stream, queue)

diff_proc(proc, arg)

diff_rec(pos, diffs)