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##
## Datastructures: GAP package providing common datastructures.
##
## Copyright (C) 2015-2017 The datastructures team.
## For list of the team members, please refer to the COPYRIGHT file.
##
## This package is licensed under the GPL 2 or later, please refer
## to the COPYRIGHT.md and LICENSE files for details.
##
##
## This file defines stacks.
##
InstallGlobalFunction(Stack,
function()
return Objectify(StackTypeMutable, [ [] ]);
end);
InstallMethod(Push
, "for a stack"
, [IsStack, IsObject],
function(s,o)
Add(s![1], o);
end);
InstallMethod(Peek
, "for a stack"
, [IsStack],
function(s)
if Length(s![1]) > 0 then
return s![1][Length(s![1])];
else
return fail;
fi;
end);
InstallMethod(Pop
, "for a stack"
, [IsStack],
function(s)
if Length(s![1]) > 0 then
return Remove(s![1]);
else
return fail;
fi;
end);
InstallOtherMethod(Size
, "for a stack"
, [IsStack]
, s -> Length(s![1]));
InstallMethod(ViewString
, "for a stack"
, [IsStack],
function(s)
return STRINGIFY("<stack with ", Length(s![1]), " entries>");
end);
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