candran/compiler/lua53.can

return function(code, ast, options)
	--- Line mapping
	local lastInputPos = 1 -- last token position in the input code
	local prevLinePos = 1 -- last token position in the previous line of code in the input code
	local lastSource = "nil" -- last found code source name (from the original file)
	local lastLine = 1 -- last found line number (from the original file)

	--- Newline management
	local indentLevel = 0
	-- Returns a newline.
	local function newline()
		local r = options.newline .. string.rep(options.indentation, indentLevel)
		if options.mapLines then
			local sub = code:sub(lastInputPos)
			local source, line = sub:sub(1, sub:find("\n")):match("%-%- (.-)%:(%d+)\n")

			if source and line then
				lastSource = source
				lastLine = tonumber(line)
			else
				for _ in code:sub(prevLinePos, lastInputPos):gmatch("\n") do
					lastLine += 1
				end
			end

			prevLinePos = lastInputPos

			r = " -- " .. lastSource .. ":" .. lastLine .. r
		end
		return r
	end
	-- Returns a newline and add one level of indentation.
	local function indent()
		indentLevel += 1
		return newline()
	end
	-- Returns a newline and remove one level of indentation.
	local function unindent()
		indentLevel -= 1
		return newline()
	end

	--- Module management
	local required = {} -- { ["module"] = true, ... }
	local requireStr = ""
	-- Add the module "mod" to the list of modules to require, and load its field "field" (or the whole module if nil) into the variable "name".
	local function addRequire(mod, name, field)
		if not required[mod] then
			requireStr ..= "local " .. options.requirePrefix .. name .. (" = require(%q)"):format(mod) .. (field and "."..field or "") .. options.newline
			required[mod] = true
		end
	end
	-- Returns the required module variable name.
	local function getRequire(name)
		return options.requirePrefix .. name
	end

	--- AST traversal helpers
	-- Returns the first node from the list "list" which tag is in the list "tags", or nil if there were none.
	local function any(list, tags)
		local tagsCheck = {}
		for _, tag in ipairs(tags) do
			tagsCheck[tag] = true
		end
		for _, node in ipairs(list) do
			if tagsCheck[node.tag] then
				return node
			end
		end
		return nil
	end

	--- Modification helpers
	local namedNodes = {} -- { ["name"] = ast, ... }
	-- Wrap the compiled code of a named node with suffix and prefix.
	local function wrap(name, prefix, suffix)
		local node = namedNodes[name]
		if not node then error("not inside a " .. name) end
		node.prefix, node.suffix = prefix .. newline(), newline() .. suffix
	end

	--- Lua compiler
	local tags
	-- Recursively returns the compiled AST Lua code, set "forceTag" to override the tag type and pass additional arguments to the tag constructor if needed.
	local function lua(ast, forceTag, ...)
		if options.mapLines and ast.pos then
			lastInputPos = ast.pos
		end
		return tags[forceTag or ast.tag](ast, ...)
	end
	-- Same as lua(), but gives the AST node a name which can be used for further access & modification.
	local function namedLua(name, ast, ...)
		local old = namedNodes[name]
		namedNodes[name] = ast
		local code = lua(ast, ...)
		namedNodes[name] = old
		return (ast.prefix or "") .. code .. (ast.suffix or "")
	end
	-- Tag constructors
	tags = setmetatable({
		-- block: { stat* } --
		Block = (t)
			local r = ""
			for i=1, #t-1, 1 do
				r ..= lua(t[i]) .. newline()
			end
			if t[#t] then
				r ..= lua(t[#t])
			end
			return r
		end,

		-- stat --

		-- Do{ stat* }
		Do = (t)
			return "do" .. indent() .. lua(t, "Block") .. unindent() .. "end"
		end,
		-- Set{ {lhs+} (opid? = opid?)? {expr+} }
		Set = (t)
			if #t == 2 then
				return lua(t[1], "_lhs") .. " = " .. lua(t[2], "_lhs")
			elseif #t == 3 then
				return lua(t[1], "_lhs") .. " = " .. lua(t[3], "_lhs")
			elseif #t == 4 then
				if t[3] == "=" then
					local r = lua(t[1], "_lhs") .. " = " .. lua({ t[2], t[1][1], { tag = "Paren", t[4][1] } }, "Op")
					for i=2, math.min(#t[4], #t[1]), 1 do
						r ..= ", " .. lua({ t[2], t[1][i], { tag = "Paren", t[4][i] } }, "Op")
					end
					return r
				else
					local r = lua(t[1], "_lhs") .. " = " .. lua({ t[3], { tag = "Paren", t[4][1] }, t[1][1] }, "Op")
					for i=2, math.min(#t[4], #t[1]), 1 do
						r ..= ", " .. lua({ t[3], { tag = "Paren", t[4][i] }, t[1][i] }, "Op")
					end
					return r
				end
			else -- You are mad.
				local r = lua(t[1], "_lhs") .. " = " .. lua({ t[2], t[1][1], { tag = "Op", t[4], { tag = "Paren", t[5][1] }, t[1][1] } }, "Op")
				for i=2, math.min(#t[5], #t[1]), 1 do
					r ..= ", " .. lua({ t[2], t[1][i], { tag = "Op", t[4], { tag = "Paren", t[5][i] }, t[1][i] } }, "Op")
				end
				return r
			end
		end,
		-- While{ expr block }
		While = (t)
			return "while " .. lua(t[1]) .. " do" .. indent() .. namedLua("loop", t[2]) .. unindent() .. "end"
		end,
		-- Repeat{ block expr }
		Repeat = (t)
			return "repeat".. indent() .. namedLua("loop", t[1]) .. unindent() .. "until " .. lua(t[2])
		end,
		-- If{ (expr block)+ block? }
		If = (t)
			local r = "if " .. lua(t[1]) .. " then" .. indent() .. lua(t[2]) .. unindent()
			for i=3, #t-1, 2 do
				r ..= "elseif " .. lua(t[i]) .. " then" .. indent() .. lua(t[i+1]) .. unindent()
			end
			if #t % 2 == 1 then
				r ..= "else" .. indent() .. lua(t[#t]) .. unindent()
			end
			return r .. "end"
		end,
		-- Fornum{ ident expr expr expr? block }
		Fornum = (t)
			local r = "for " .. lua(t[1]) .. " = " .. lua(t[2]) .. ", " .. lua(t[3])
			if #t == 5 then
				return r .. ", " .. lua(t[4]) .. " do" .. indent() .. lua(t[5]) .. unindent() .. "end"
			else
				return r .. " do" .. indent() .. namedLua("loop", t[4]) .. unindent() .. "end"
			end
		end,
		-- Forin{ {ident+} {expr+} block }
		Forin = (t)
			return "for " .. lua(t[1], "_lhs") .. " in " .. lua(t[2], "_lhs") .. " do" .. indent() .. namedLua("loop", t[3]) .. unindent() .. "end"
		end,
		-- Local{ {ident+} {expr+}? }
		Local = (t)
			local r = "local "..lua(t[1], "_lhs")
			if t[2][1] then
				r ..= " = "..lua(t[2], "_lhs")
			end
			return r
		end,
		-- Let{ {ident+} {expr+}? }
		Let = (t)
			local nameList = lua(t[1], "_lhs")
			local r = "local " .. nameList
			if t[2][1] then
				if any(t[2], { "Function", "Table", "Paren" }) then -- predeclaration doesn't matter otherwise
					r ..= newline() .. nameList .. " = " .. lua(t[2], "_lhs")
				else
					r ..= " = " .. lua(t[2], "_lhs")
				end
			end
			return r
		end,
		-- Localrec{ ident expr }
		Localrec = (t)
			return "local function "..lua(t[1][1])..lua(t[2][1], "_functionWithoutKeyword")
		end,
		-- Goto{ <string> }
		Goto = (t)
			return "goto " .. lua(t[1], "Id")
		end,
		-- Label{ <string> }
		Label = (t)
			return "::" .. lua(t[1], "Id") .. "::"
		end,
		-- Return{ <expr*> }
		Return = (t)
			return "return "..lua(t, "_lhs")
		end,
		-- Break
		Break = ()
			return "break"
		end,
		-- Continue
		Continue = ()
			wrap("loop", "repeat", "until true")
			return "break"
		end,
		-- apply (below)

		-- expr --

		-- Nil
		Nil = ()
			return "nil"
		end,
		-- Dots
		Dots = ()
			return "..."
		end,
		-- Boolean{ <boolean> }
		Boolean = (t)
			return tostring(t[1])
		end,
		-- Number{ <number> }
		Number = (t)
			return tostring(t[1])
		end,
		-- String{ <string> }
		String = (t)
			return ("%q"):format(t[1])
		end,
		-- Function{ { ( `ParPair{ Id expr } | `Id{ <string> } )* `Dots? } block }
		_functionWithoutKeyword = (t)
			local r = "("
			local decl = {}
			if t[1][1] then
				if t[1][1].tag == "ParPair" then
					local id = lua(t[1][1][1])
					indentLevel += 1
					table.insert(decl, id .. " = " .. id .. " == nil and " .. lua(t[1][1][2]) .. " or " .. id)
					indentLevel -= 1
					r ..= id
				else
					r ..= lua(t[1][1])
				end
				for i=2, #t[1], 1 do
					if t[1][i].tag == "ParPair" then
						local id = lua(t[1][i][1])
						indentLevel += 1
						table.insert(decl, "if " .. id .. " == nil then " .. id .. " = " .. lua(t[1][i][2]) .. " end")
						indentLevel -= 1
						r ..= ", " ..id
					else
						r ..= ", " .. lua(t[1][i])
					end
				end
			end
			r ..= ")" .. indent()
			for _, d in ipairs(decl) do
				r ..= d .. newline()
			end
			return r .. lua(t[2]) .. unindent() .. "end"
		end,
		Function = (t)
			return "function" .. lua(t, "_functionWithoutKeyword")
		end,
		-- Table{ ( `Pair{ expr expr } | expr )* }
		Pair = (t)
			return "[" .. lua(t[1]) .. "] = " .. lua(t[2])
		end,
		Table = (t)
			if #t == 0 then
				return "{}"
			elseif #t == 1 then
				return "{ " .. lua(t, "_lhs") .. " }"
			else
				return "{" .. indent() .. lua(t, "_lhs") .. unindent() .. "}"
			end
		end,
		-- Op{ opid expr expr? }
		Op = (t)
			local r
			if #t == 2 then
				if type(tags._opid[t[1]]) == "string" then
					r = tags._opid[t[1]] .. " " .. lua(t[2])
				else
					r = tags._opid[t[1]](t[2])
				end
			else
				if type(tags._opid[t[1]]) == "string" then
					r = lua(t[2]) .. " " .. tags._opid[t[1]] .. " " .. lua(t[3])
				else
					r = tags._opid[t[1]](t[2], t[3])
				end
			end
			return r
		end,
		-- Paren{ expr }
		Paren = (t)
			return "(" .. lua(t[1]) .. ")"
		end,
		-- DoExpr{ stat* }
		DoExpr = (t)
			return "(function()" .. indent() .. lua(t, "Do") .. unindent() .. "end)()"
		end,
		-- WhileExpr{ expr block }
		WhileExpr = (t)
			return "(function()" .. indent() .. lua(t, "While") .. unindent() .. "end)()"
		end,
		-- RepeatExpr{ expr block }
		RepeatExpr = (t)
			return "(function()" .. indent() .. lua(t, "Repeat") .. unindent() .. "end)()"
		end,
		-- IfExpr{ (expr block)+ block? }
		IfExpr = (t)
			return "(function()" .. indent() .. lua(t, "If") .. unindent() .. "end)()"
		end,
		-- FornumExpr{ ident expr expr expr? block }
		FornumExpr = (t)
			return "(function()" .. indent() .. lua(t, "Fornum") .. unindent() .. "end)()"
		end,
		-- Forin{ {ident+} {expr+} block }
		ForninExpr = (t)
			return "(function()" .. indent() .. lua(t, "Forin") .. unindent() .. "end)()"
		end,
		-- apply (below)
		-- lhs (below)

		-- apply --

		-- Call{ expr expr* }
		Call = (t)
			return lua(t[1]) .. "(" .. lua(t, "_lhs", 2) .. ")"
		end,

		-- Invoke{ expr `String{ <string> } expr* }
		Invoke = (t)
			return lua(t[1])..":"..lua(t[2], "Id").."("..lua(t, "_lhs", 3)..")"
		end,

		-- lhs --
		_lhs = (t, start)
			start = start or 1
			local r
			if t[start] then
				r = lua(t[start])
				for i=start+1, #t, 1 do
					r ..= ", "..lua(t[i])
				end
			else
				r = ""
			end
			return r
		end,
		-- Id{ <string> }
		Id = (t)
			return t[1]
		end,
		-- Index{ expr expr }
		Index = (t)
			return lua(t[1]).."["..lua(t[2]).."]"
		end,

		-- opid --
		_opid = {
			add = "+", sub = "-", mul = "*", div = "/",
			idiv = "//", mod = "%", pow = "^", concat = "..",
			band = "&", bor = "|", bxor = "~", shl = "<<", shr = ">>",
			eq = "==", ne = "~=", lt = "<", gt = ">", le = "<=", ge = ">=",
			["and"] = "and", ["or"] = "or", unm = "-", len = "#", bnot = "~", ["not"] = "not"
		}
	}, {
		__index = (self, key)
			error("don't know how to compile a "..tostring(key).." to Lua 5.3")
		end
	})

	#placeholder("patch")

	local code = lua(ast) .. newline()
	return requireStr .. code
end