Ch6, Ex10

Swap code impl with call by need:

declare
proc {Swap X Y}
   Xarg = {X}
   Yarg = {Y}
   T = {NewCell @Xarg}
in
   Xarg:=@Yarg
   Yarg:=@T
end 

Counterintuitive behavior does not occur with this version.

Sqr code call by need impl with using laziness:

declare
proc {Sqr A}
   B={A}
in
   B:=@B*@B
end

local C={NewCell 0} in
   C:=25
   %made the argument function lazy
   {Sqr fun lazy {$} C end}
   {Browse @C}
end