modns: [+] add subloader helper for abstracting access to sub-components

modns/construct_interface.lua

@@ -8,6 +8,7 @@ return function(loader)
 	local modns = {
 		get = mtrequire,
 		mk_parent_ns = nsauto.ns,
+		create_subloader = nsauto.create_subloader,
 	}
 
 	return modns

modns/nsauto.lua

@@ -2,6 +2,11 @@
 local mk_helpers = function(loader)
 
 
+
+local create_subloader = (dofile(_modpath.."subloader.lua"))(loader)
+
+
+
 local dname = "mk_parent_ns_noauto() "
 local mk_parent_ns_noauto_inner = function(list, base, sep)
 	local result = {}
@@ -23,6 +28,7 @@ end
 
 return {
 	ns = mk_parent_ns,
+	create_subloader = create_subloader,
 }
 
 

modns/subloader.lua

@@ -0,0 +1,53 @@
+--[[
+A subloader represents an abstraction of accessing sub-components of a given path.
+You can pass it a list of sub-path segments
+(e.g. {"some", "child"} as opposed to "some.child")
+or a single segment string to load a component relative to a base path;
+this base path is baked into the subloader at construction time.
+]]
+
+
+
+
+-- concat a path passed as a table of components,
+-- or accept just a string to act as a list of length one.
+-- data SubPath = Single Segment | Deep [Segment]
+-- concat_path :: SubPath -> PathSep -> SubPathStr
+local msg_concat = "path concatenation: expected a string or table, got "
+local concat_path = function(path, sep)
+	local t = type(path)
+	if t == "string" then
+		return path
+	elseif t == "table" then
+		return table.concat(path, sep)
+	else
+		error(msg_concat .. t)
+	end
+end
+
+
+
+
+
+local checkstr = function(v) assert(type(v) == "string") end
+
+-- it's closures all the way dooooooooown
+local attach_loader = function(loader)
+	local create_subloader = function(base, sep)
+		checkstr(base)
+		checkstr(sep)
+		base = base .. sep
+
+		return function(subpath)
+			local subs = concat_path(subpath, sep)
+			local fullpath = base..subs
+			return loader:get(fullpath)
+		end
+	end
+	return create_subloader
+end
+
+
+
+return attach_loader
+