From cb0111b2904d1c01885a1e739a3dae5f31a41673 Mon Sep 17 00:00:00 2001
From: David Given <dg@cowlark.com>
Date: Mon, 6 Jun 2016 20:50:48 +0200
Subject: [PATCH] Skeleton of the rule engine and type system.

---
 first/ackbuilder.lua | 170 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 153 insertions(+), 17 deletions(-)

diff --git a/first/ackbuilder.lua b/first/ackbuilder.lua
index 1ac37350f..301078c6d 100644
--- a/first/ackbuilder.lua
+++ b/first/ackbuilder.lua
@@ -8,6 +8,10 @@
 
 local environment = {}
 local rules = {}
+local targets = {}
+local buildfiles = {}
+local globals
+local cwd = "."
 
 local function subenv(old, cb)
 	if not old then
@@ -49,37 +53,169 @@ local function emit(...)
 	end
 end
 
-local function definerule(name, cb)
-	if rules[name] then
-		error(string.format("rule '%s' is already defined", name))
+local function loadbuildfile(filename)
+	local data, chunk, e
+	data = io.open(filename):read("*a")
+	if not e then
+		local thisglobals = {_G = thisglobals}
+		setmetatable(thisglobals, {__index = globals})
+		chunk, e = loadstring(data, filename, "text", thisglobals)
+	end
+	if e then
+		error(string.format("couldn't load '%s': %s", filename, e))
+	end
+
+	chunk()
+end
+
+local function loadtarget(targetname)
+	if targets[target] then
+		return targets[targetname]
+	end
+
+	local target
+	if not target:find(":") then
+		target = {
+			outs = {targetname},
+			is = {
+				__implicitfile = true
+			}
+		}
+		targets[targetname] = target
+	else
+		local _, _, filepart, targetpart = targetname:find("^([^:]+):(%w+)$")
+		if not filepart or not targetpart then
+			error(string.format("malformed target name '%s'", targetname))
+		end
+		if not buildfiles[filepart] then
+			buildfiles[filepart] = true
+
+			local oldcwd = cwd
+			cwd = filepart
+			loadbuildfile(filepart.."/build.lua")
+			cwd = oldcwd
+		end
+
+		target = targets[targetname]
+		if not target then
+			error(string.format("build file '%s' contains no rule '%s'",
+				filepart, targetpart))
+		end
+	end
+
+	return target
+end
+
+local typeconverters = {
+	targets = function(propname, i)
+		if (type(i) == "string") then
+			i = {i}
+		elseif (type(i) ~= "table") then
+			error(string.format("property '%s' must be a target list", propname))
+		end
+
+		local o = {}
+		for _, s in ipairs(i) do
+			if (type(s) ~= "string") then
+				error(string.format("member of target list '%s' is not a string", propname))
+			end
+
+			if s:find("^//") then
+				s = s:gsub("^//", "")
+			elseif s:find("^[/]") then
+				s = concatpath(cwd, s)
+			end
+			o[#o+1] = s
+		end
+	end,
+
+	strings = function(propname, i)
+		if (type(i) == "string") then
+			i = {i}
+		elseif (type(i) ~= "table") then
+			error(string.format("property '%s' must be a string list", propname))
+		end
+
+		return i
+	end,
+
+	string = function(propname, i)
+		if (type(i) ~= "string") then
+			error(string.format("property '%s' must be a string", propname))
+		end
+	end,
+}
+	
+local function definerule(rulename, types, cb)
+	if rules[rulename] then
+		error(string.format("rule '%s' is already defined", rulename))
+	end
+
+	types.name = { type="string" }
+
+	for propname, typespec in pairs(types) do
+		if not typeconverters[typespec.type] then
+			error(string.format("property '%s' has unrecognised type '%s'",
+				propname, typespec.type))
+		end
+	end
+
+	rules[rulename] = function(e)
+		local args = {}
+		for propname, typespec in pairs(types) do
+			if not e[propname] and not typespec.optional then
+				error(string.format("missing mandatory property '%s'", propname))
+			end
+
+			args[propname] = typeconverters[typespec.type](propname, e[propname])
+			e[propname] = nil
+		end
+
+		local propname, _ = next(e)
+		if propname then
+			error(string.format("don't know what to do with property '%s'", propname))
+		end
 	end
 end
 
+-----------------------------------------------------------------------------
+--                              DEFAULT RULES                              --
+-----------------------------------------------------------------------------
+
+definerule("simplerule",
+	{
+		ins = { type="targets" },
+		outs = { type="strings" },
+	},
+	function (e)
+	end
+)
+
 -----------------------------------------------------------------------------
 --                               MAIN PROGRAM                              --
 -----------------------------------------------------------------------------
 
-local globals = {
+globals = {
 	asstring = asstring,
 	definerule = definerule,
 	emit = emit,
 	environment = environment,
 }
-setmetatable(globals, {__index = _G})
+setmetatable(globals,
+	{
+		__index = function(self, k)
+			local rule = rules[k]
+			if rule then
+				return rule
+			else
+				return _G[k]
+			end
+		end
+	}
+)
 
 emit("hide=@\n")
 for _, file in ipairs({...}) do
-	local data, chunk, e
-	data = io.open(file):read("*a")
-	if not e then
-		local thisglobals = {_G = thisglobals}
-		setmetatable(thisglobals, {__index = globals})
-		chunk, e = loadstring(data, file, "text", thisglobals)
-	end
-	if e then
-		error(string.format("couldn't load '%s': %s", file, e))
-	end
-
-	local _, e = pcall(chunk)
+	loadbuildfile(file)
 end
 
-- 
2.34.1