Lua 3.13.1

1 files changed, 55 insertions, 0 deletions

diff --git a/etc/setfallback.lua b/etc/setfallback.lua
new file mode 100644
index 00000000..783b8667
--- /dev/null
+++ b/etc/setfallback.lua
@@ -0,0 +1,55 @@
+--------------------------------------------------------------
+-- 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