More bigint type checks added

Strict checking is still off, however a check can be coerced

libs/bigint/bigint.lua

@@ -8,27 +8,7 @@ local strict = false
 
 local bigint = {}
 
-local named_powers = require("libs.bigint.named-powers-of-ten")
-
--- Create a new bigint or convert a number or string into a big
--- Returns an empty, positive bigint if no number or string is given
-function bigint.new(num)
-    local self = {
-        sign = "+",
-        digits = {}
-    }
-
-    -- Return a new bigint with the same sign and digits
-    function self:clone()
-        local newint = bigint.new()
-        newint.sign = self.sign
-        for _, digit in pairs(self.digits) do
-            newint.digits[#newint.digits + 1] = digit
-        end
-        return newint
-    end
-
-    setmetatable(self, {
+local mt = {
     __add = function(lhs, rhs)
         return bigint.add(lhs, rhs)
     end,
@@ -53,7 +33,29 @@ function bigint.new(num)
     __tostring = function()
         return bigint.unserialize(self, "s")
     end
-    })
+}
+
+local named_powers = require("libs.bigint.named-powers-of-ten")
+
+-- Create a new bigint or convert a number or string into a big
+-- Returns an empty, positive bigint if no number or string is given
+function bigint.new(num)
+    local self = {
+        sign = "+",
+        digits = {}
+    }
+
+    -- Return a new bigint with the same sign and digits
+    function self:clone()
+        local newint = bigint.new()
+        newint.sign = self.sign
+        for _, digit in pairs(self.digits) do
+            newint.digits[#newint.digits + 1] = digit
+        end
+        return newint
+    end
+
+    setmetatable(self, mt)
 
     if (num) then
         local num_string = tostring(num)
@@ -73,10 +75,11 @@ end
 -- forced by supplying "true" as the second argument.
 function bigint.check(big, force)
     if (strict or force) then
+        assert(getmetatable(big) == mt, "at least one arg is not a bigint")
         assert(#big.digits > 0, "bigint is empty")
-        assert(type(big.sign) == "string", "bigint is unsigned")
+        assert(big.sign == "+" or big.sign == "-", "bigint is unsigned")
         for _, digit in pairs(big.digits) do
-            assert(type(digit) == "number", digit .. " is not a number")
+            assert(type(digit) == "number", "at least one digit is invalid")
             assert(digit <= 9 and digit >= 0, digit .. " is not between 0 and 9")
             assert(math.floor(digit) == digit, digit .. " is not an integer")
         end