# Derived from `The Icon Programming Language', (1st edn, Ch13 s13.4.2 p139)
#
# coexpressions:  create, @
#
# A: replace aa by b          B: replace bb by c
# reads---->A-------------------------->B-------------->writes
#           aa... -> b... |            |bb... -> |c...
#           ax... -> ax...|----------->|bz... -> |bz...
#           x...  -> x... |            |x...  -> |x...

global A, B

procedure main()
   A := create compact("a", "b", create |reads(), B)  # coexpression A
#                      s1   s2   ------in------- out
   B := create compact("b", "c", A, &main)            # coexpression B
#                      s1   s2  in  -out-
   write("type input lines, try single and multiple a's and b's")
   while writes(@B)
end

procedure compact(s1, s2, in, out)  # compact two s1's into an s2
   local s
   while s := @in do
      { if s == s1 then
           { s := @in
             if s == s1 then # <s1><s1> -> <s2>
                  s := s2
             else s1 @ out   # <s1><~s1> -> <s1><~s1>
           }
         s @ out
      }
end

#\fB Example of Coexpressions. \fP