add check and radio controls

luigi/widget/check.lua

@@ -0,0 +1,18 @@
+--[[--
+A check box.
+
+@widget check
+--]]--
+
+return function (self)
+    self:onPress(function ()
+        self.value = not self.value
+    end)
+
+    self:onChange(function ()
+        local subtype = self.value and 'check.checked' or 'check.unchecked'
+        self.type = { 'check', subtype }
+    end)
+
+    self.value = not not self.value
+end

luigi/widget/radio.lua

@@ -0,0 +1,33 @@
+--[[--
+A radio button.
+
+@widget radio
+--]]--
+
+-- TODO: make `group` a first-class attribute
+local groups = {}
+
+return function (self)
+    local groupName = self.group or 'default'
+
+    if not groups[groupName] then
+        groups[groupName] = {}
+    end
+
+    local group = groups[groupName]
+
+    group[#group + 1] = self
+
+    self:onPress(function ()
+        for _, widget in ipairs(group) do
+            widget.value = widget == self
+        end
+    end)
+
+    self:onChange(function ()
+        local subtype = self.value and 'radio.checked' or 'radio.unchecked'
+        self.type = { 'radio', subtype }
+    end)
+
+    self.value = not not self.value
+end