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############################################################################
#
#	File:     scanmodl.icn
#
#	Subject:  Procedures to model string scanning
#
#	Author:   Ralph E. Griswold
#
#	Date:     May 30, 1993
#
############################################################################
#
#   This file is in the public domain.
#
############################################################################
#
#  These procedures model string scanning:
#
#	e1 ? e2 -> Escan(Bscan(e1, e2)
#
#  See Icon Analyst 6, pp. 1-2.
#
############################################################################

record ScanEnvir(subject, pos)

procedure Bscan(e1)
   local OuterEnvir
   OuterEnvir := ScanEnvir(&subject, &pos)
   &subject := e1
   &pos := 1
   suspend OuterEnvir
   &subject := OuterEnvir.subject
   &pos := OuterEnvir.pos
   fail
end

procedure Escan(OuterEnvir, e2)
   local InnerEnvir
   InnerEnvir := ScanEnvir(&subject, &pos)
   &subject := OuterEnvir.subject
   &pos := OuterEnvir.pos
   suspend e2
   OuterEnvir.subject := &subject
   OuterEnvir.pos := &pos
   &subject := InnerEnvir.subject
   &pos := InnerEnvir.pos
   fail
end