diff --git a/src/core/org/luaj/lib/TableLib.java b/src/core/org/luaj/lib/TableLib.java
index b502cd67..13eab744 100644
--- a/src/core/org/luaj/lib/TableLib.java
+++ b/src/core/org/luaj/lib/TableLib.java
@@ -96,10 +96,10 @@ public class TableLib extends LFunction {
 		 */
 		case CONCAT: { 
 			int n = vm.gettop();
-			LTable table = vm.totable(2);
-			LString sep = (n>=3? vm.tolstring(3): null);
-			int i = (n>=4? vm.tointeger(4): 1);
-			int j = (n>=5? vm.tointeger(5): table.luaLength());
+			LTable table = vm.checktable(2);
+			LString sep = (n>=3? vm.checklstring(3): null);
+			int i = (n>=4? vm.checkint(4): 1);
+			int j = (n>=5? vm.checkint(5): table.luaLength());
 			ByteArrayOutputStream baos = new ByteArrayOutputStream();
 			for ( int k=i; k<=j; k++ ) {
 				LValue v = table.get(k);
@@ -119,8 +119,8 @@ public class TableLib extends LFunction {
 		case FOREACH: 
 		case FOREACHI: 
 		{ 
-			LTable table = vm.totable(2);
-			LFunction function = vm.tojavafunction(3);
+			LTable table = vm.checktable(2);
+			LFunction function = vm.checkfunction(3);
 			LValue result = table.foreach( vm, function, id==FOREACHI );
 			vm.resettop();
 			vm.pushlvalue( result );
@@ -132,7 +132,7 @@ public class TableLib extends LFunction {
 		 * Get length of table t.
 		 */ 
 		case GETN: { 
-			LTable table = vm.totable(2);
+			LTable table = vm.checktable(2);
 			vm.resettop();
 			vm.pushinteger(table.luaLength());
 			break;
@@ -146,10 +146,11 @@ public class TableLib extends LFunction {
 		 */ 
 		case INSERT: { 
 			int n = vm.gettop();
-			LTable table = vm.totable(2);
-			int pos = (n>=4? vm.tointeger(3): 0);
+			LTable table = vm.checktable(2);
+			int pos = (n>=4? vm.checkint(3): 0);
 			LValue value = vm.topointer(-1);
 			table.luaInsertPos( pos, value );
+			vm.resettop();
 			break;
 		}
 
@@ -159,7 +160,7 @@ public class TableLib extends LFunction {
 		 * indices. (To do its job this function does a linear traversal of the whole table.)
 		 */ 
 		case MAXN: { 
-			LTable table = vm.totable(2);
+			LTable table = vm.checktable(2);
 			vm.resettop();
 			vm.pushlvalue( table.luaMaxN() );
 			break;
@@ -173,8 +174,8 @@ public class TableLib extends LFunction {
 		 */ 
 		case REMOVE: {
 			int n = vm.gettop();
-			LTable table = vm.totable(2);
-			int pos = (n>=3? vm.tointeger(3): 0);
+			LTable table = vm.checktable(2);
+			int pos = (n>=3? vm.checkint(3): 0);
 			vm.resettop();
 			LValue removed = table.luaRemovePos( pos );
 			if ( removed != LNil.NIL )
@@ -192,8 +193,8 @@ public class TableLib extends LFunction {
 		 * The sort algorithm is not stable; that is, elements considered equal by the given order may have their relative positions changed by the sort.
 		 */ 
 		case SORT: { 
-			LTable table = vm.totable(2);
-			LValue compare = vm.topointer(3);
+			LTable table = vm.checktable(2);
+			LValue compare = vm.checkfunction(3);
 			table.luaSort( vm, compare );
 			vm.resettop();
 			break;
diff --git a/src/core/org/luaj/vm/LNumber.java b/src/core/org/luaj/vm/LNumber.java
index 457064d2..759b0caf 100644
--- a/src/core/org/luaj/vm/LNumber.java
+++ b/src/core/org/luaj/vm/LNumber.java
@@ -45,6 +45,13 @@ public class LNumber extends LValue {
 	 */
 	public abstract boolean isInteger();
 	
+	/** 
+	 * In lua all numbers are strings !
+	 */
+	public boolean isString() {
+		return true;
+	}
+
 	/** Convert to a Byte value */
 	public Byte toJavaBoxedByte() {
 		return new Byte(toJavaByte());
diff --git a/src/core/org/luaj/vm/LuaState.java b/src/core/org/luaj/vm/LuaState.java
index 7644148d..85710455 100644
--- a/src/core/org/luaj/vm/LuaState.java
+++ b/src/core/org/luaj/vm/LuaState.java
@@ -2614,14 +2614,14 @@ public class LuaState extends Lua {
 
     // ================= Error Reporting Functions =================
 
-    /**
-     * Report an error with an argument.
-     * 
-     * @param narg
-     *            Stack index of the bad argument
-     * @param extramsg
-     *            String to include in error message
-     */
+	/**
+	 * Report an error with an argument.
+	 * 
+	 * @param narg
+	 *            Stack index of the bad argument
+	 * @param extramsg
+	 *            String to include in error message
+	 */
     public void argerror(int narg, String extramsg) {
         // TODO: port ldebug.c and provide mode useful error messages.
         error("bad argument #" + (narg - 1) + " (" + extramsg + ")");
@@ -2651,6 +2651,136 @@ public class LuaState extends Lua {
     public void typerror(int narg, int typenum) {
         typerror(narg, TYPE_NAMES[typenum]);
     }
+    
+
+	/**
+	 * Checks whether the function has an argument of any type (including <b>nil</b>)
+	 * at position <code>narg</code>.
+	 * @param narg the argument number
+	 * @throws LuaErrorException if there is no argument at position narg
+	 */
+	public void checkany(int narg) {
+		if ( gettop() < narg )
+			argerror(narg, "value expected");
+	}
+
+	/**
+	 * Checks whether the function argument <code>narg</code> is a function and
+	 * returns this function.
+	 * @see LFunction
+	 * @param narg the argument number
+	 * @throws LuaErrorException if the value is not a function
+	 * @return LFunction value if the argument is a function
+	 */
+	public LFunction checkfunction(int narg) {
+		return (LFunction) checktype(narg, Lua.LUA_TFUNCTION);
+	}
+	
+	/**
+	 * Checks whether the function argument <code>narg</code> is a number and
+	 * returns this number cast to an <code>int</code>.
+	 * @param narg the argument number
+	 * @throws LuaErrorException if the number cannot be converted to an int
+	 * @return int value if the argument is an int or can be converted to one
+	 */
+	public int checkint(int narg) {
+		LValue v = tolnumber(narg);
+		if ( ! v.isInteger() )
+			typerror(narg, Lua.LUA_TNUMBER);
+		return v.toJavaInt();
+	}
+
+	/**
+	 * Checks whether the function argument <code>narg</code> is a number and
+	 * returns this number cast to a <code>LInteger</code></a>.
+	 * @see LInteger
+	 * @param narg the argument number
+	 * @throws LuaErrorException if the value cannot be converted to an int
+	 * @return LInteger value if the argument is an int or can be converted to one
+	 */
+	public LInteger checkinteger(int narg) {
+		return LInteger.valueOf(checkint(narg));
+	}
+	
+	/**
+	 * Checks whether the function argument <code>narg</code> is a number and
+	 * returns this number cast to a <code>long</code>.
+	 * @param narg the argument number
+	 * @throws LuaErrorException if the value cannot be converted to a long
+	 * @return long value if the argument is a number or can be converted to long
+	 */
+	public long checklong(int narg) {
+		return checknumber(narg).toJavaLong();
+	}
+
+	/**
+	 * Checks whether the function argument <code>narg</code> is a number and
+	 * returns this number.
+	 * @see LNumber
+	 * @param narg the argument number
+	 * @throws LuaErrorException if the value cannot be converted to a number
+	 * @return LNumber value if the argument is a number or can be converted to one
+	 */
+	public LNumber checknumber(int narg) {
+		return (LNumber) checktype(narg, Lua.LUA_TTABLE);
+	}
+	
+	/**
+	 * Checks whether the function argument <code>narg</code> is a string and
+	 * returns this string as a lua string.
+	 * @see LString
+	 * @param narg the argument number
+	 * @throws LuaErrorException if the value cannot be converted to a string
+	 * @return LString value if the argument is a string or can be converted to one
+	 */
+	public LString checklstring(int narg) {
+		LValue v = topointer(narg);
+		if ( ! v.isString() )
+			typerror(narg, Lua.LUA_TSTRING);
+		return v.luaAsString();
+	}
+
+	/**
+	 * Checks whether the function argument <code>narg</code> is a string and
+	 * returns this string as a Java String.
+	 * @param narg the argument number
+	 * @throws LuaErrorException if the value cannot be converted to a string
+	 * @return String value if the argument is a string or can be converted to one
+	 */
+	public String checkstring(int narg) {
+		LValue v = topointer(narg);
+		if ( ! v.isString() )
+			typerror(narg, Lua.LUA_TSTRING);
+		return v.toJavaString();
+	}
+
+	/**
+	 * Checks whether the function argument <code>narg</code> is a table and
+	 * returns this table.
+	 * @see LTable
+	 * @param narg the argument number
+	 * @throws LuaErrorException if the value is not a table
+	 * @return LTable value if the argument is a table
+	 */
+	public LTable checktable(int narg) {
+		return (LTable) checktype(narg, Lua.LUA_TTABLE);
+	}
+	
+	/**
+	 * Checks whether the function argument <code>narg</code> has type
+	 * <code>t</code> and return it as an LValue.
+	 * @param narg the argument number
+	 * @param t the type number to check against
+	 * @return the lua value
+	 * @throws LuaErrorException if the value is not of type t
+	 */
+	public LValue checktype(int narg, int t) {
+		LValue v = topointer(narg);
+		if ( v.luaGetType() != t )
+			typerror(narg, t);
+		return v;
+	}
+
 
     /**
      * Check that the type of userdata on the stack matches the required type,
diff --git a/src/test/errors/args.lua b/src/test/errors/args.lua
index a935a8ed..33dc636e 100644
--- a/src/test/errors/args.lua
+++ b/src/test/errors/args.lua
@@ -52,14 +52,40 @@ local structtypes = {
 	['userdata']='<userdata>',
 }
 
-local function signature(name,arglist)
+local function bracket(v)
+	return "<"..type(v)..">"
+end
+
+local function quote(v)
+	return "'"..v.."'"
+end
+	
+local function ellipses(v)
+	local s = tostring(v)
+	return #s <= 8 and s or string.sub(s,8)..'...'
+end
+	
+local pretty = {
+	['table']=bracket,
+	['function']=bracket,
+	['thread']=bracket,
+	['userdata']=bracket,
+	['string']= quote,
+	['number']= ellipses,
+}
+
+local function values(list)
 	local t = {}
-	for i=1,#arglist do
-		local ai = arglist[i]
-		local ti = type(ai)
-		t[i] = structtypes[ti] or tostring(ai)
+	for i=1,#list do
+		local ai = list[i]
+		local fi = pretty[type(ai)]
+		t[i] = fi and fi(ai) or tostring(ai)
 	end
-	return name..'('..table.concat(t,',')..')'
+	return table.concat(t,',')
+end
+
+local function signature(name,arglist)
+	return name..'('..values(arglist)..')'
 end
 
 local function dup(t)
@@ -123,11 +149,12 @@ function checkallpass( name, typesets )
 	subbanner('checkallpass')
 	for i,v in arglists(typesets) do
 		local sig = signature(name,v)
-		local s,e = invoke( name, v )
+		local r = { invoke( name, v ) }
+		local s = table.remove( r, 1 )
 		if s then 
-			print( ok, sig )
+			print( ok, sig, values(r) )
 		else
-			print( fail, sig, e )
+			print( fail, sig, values(r) )
 		end
 	end
 end