add checks module

lib/checks.lua

@@ -0,0 +1,42 @@
+-- Copyright (c) 2006-2013 Fabien Fleutot and others.
+--
+-- All rights reserved.
+
+checkers = { }
+
+local function check_one(expected, val)
+    if type(val)==expected then return true end
+    local mt = getmetatable(val)
+    if mt and mt.__type==expected then return true end
+    local f = checkers[expected]
+    if f and f(val) then return true end
+    return false
+end
+
+local function check_many(_, expected, val)
+    if expected=='?' then return true
+    elseif expected=='!' then return (val~=nil)
+    elseif type(expected) ~= 'string' then
+        error 'strings expected by checks()'
+    elseif val==nil and expected :sub(1,1) == '?' then return true end
+    for one in expected :gmatch "[^|?]+" do
+        if check_one(one, val) then return true end
+    end
+    return false
+end
+
+local function checks(...)
+    for i, arg in ipairs{...} do
+        local name, val = debug.getlocal(2, i)
+        local success = check_many(name, arg, val)
+        if not success then
+            local fname = debug.getinfo(2, 'n').name
+            local fmt = "bad argument #%d to '%s' (%s expected, got %s)"
+            local msg = string.format(fmt, i, fname or "?", arg, type(val))
+            error(msg, 3)
+        end
+    end
+end
+
+return checks
+