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--------------------------------------------------------------
-- Definition of "setfallback" using tag methods
-- (for compatibility with old code)
--------------------------------------------------------------
-- default fallbacks for each event:
local defaults = {
gettable = function () error('indexed expression not a table') end,
settable = function () error('indexed expression not a table') end,
index = function () return nil end,
getglobal = function () return nil end,
arith = function () error('number expected in arithmetic operation') end,
order = function () error('incompatible types in comparison') end,
concat = function () error('string expected in concatenation') end,
gc = function () return nil end,
['function'] = function () error('called expression not a function') end,
error = function (s) write(_STDERR, s, '\n') end,
}
function setfallback (name, func)
-- set the given function as the tag method for all "standard" tags
-- (since some combinations may cause errors, use call to avoid messages)
local fillvalids = function (n, func)
call(settagmethod, {0, n, func}, 'x', nil)
call(settagmethod, {tag(0), n, func}, 'x', nil)
call(settagmethod, {tag(''), n, func}, 'x', nil)
call(settagmethod, {tag{}, n, func}, 'x', nil)
call(settagmethod, {tag(function () end), n, func}, 'x', nil)
call(settagmethod, {tag(settagmethod), n, func}, 'x', nil)
call(settagmethod, {tag(nil), n, func}, 'x', nil)
end
assert(type(func) == 'function')
local oldfunc
if name == 'error' then
oldfunc = seterrormethod(func)
elseif name == 'getglobal' then
oldfunc = settagmethod(tag(nil), 'getglobal', func)
elseif name == 'arith' then
oldfunc = gettagmethod(tag(0), 'pow')
foreach({"add", "sub", "mul", "div", "unm", "pow"},
function(_, n) %fillvalids(n, %func) end)
elseif name == 'order' then
oldfunc = gettagmethod(tag(nil), 'lt')
foreach({"lt", "gt", "le", "ge"},
function(_, n) %fillvalids(n, %func) end)
else
oldfunc = gettagmethod(tag(nil), name)
fillvalids(name, func)
end
return oldfunc or rawgettable(%defaults, name)
end
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