--~ a tree is a table where values with string key are properties and number keys are children

local ipairs,type=ipairs,type

local do_tree_before

do_tree_before=function(tr,fun,get_child,tp_fun)

if tp_fun(tr)~='table' then return tr end

fun(tr)

for i,v in get_child(tr) do

do_tree_before(v,fun,get_child,tp_fun)

end

return tr

end

local do_tree_after

do_tree_after=function(tr,fun,get_child,tp_fun)

if tp_fun(tr)~='table' then return tr end

for i,v in get_child(tr) do

do_tree_after(v,fun,get_child,tp_fun)

end

fun(tr)

return tr

end

local do_tree_enclose

do_tree_enclose=function(tr,pre,post,get_child,tp_fun)

if tp_fun(tr)~='table' then return tr end

pre(tr)

for i,v in get_child(tr) do

do_tree_enclose(v,pre,post,get_child,tp_fun)

end

post(tr)

return tr

end

do_tree=function(tr,pre,post)

if (not pre) and (not post) then return tr end

if not post then return do_tree_before(tr,pre,ipairs,type) end

if not pre then return do_tree_after(tr,post,ipairs,type) end

return do_tree_enclose(tr,pre,post,ipairs,type)

end

-- extend funtions

local eval_=function(l)

if type(l)~='table' then return l end

local s,r=pcall(unpack(l))

return r

end

eval_tree=function(tr,f)

return do_tree_after(tr,eval_,ipairs,type)

end

-- test

--~ local t={print,4,3,4,{tonumber,{string.format,"%d",222.0}}}

--~ eval(t)