candran/compiler/lua53.can

return function(ast, opts)
	local options = {
		indentation = "\t",
		newline = "\n",
		requirePrefix = "CANDRAN_"
	}

	local indentLevel = 0
	local function newline()
		return options.newline .. string.rep(options.indentation, indentLevel)
	end
	local function indent()
		indentLevel += 1
		return newline()
	end
	local function unindent()
		indentLevel -= 1
		return newline()
	end

	local required = {}
	local requireStr = ""
	local function addRequire(str, name, field)
		if not required[str] then
			requireStr ..= "local " .. options.requirePrefix .. name .. (" = require(%q)"):format(str) .. (field and "."..field or "") .. options.newline
			required[str] = true
		end
	end
	local function getRequire(name)
		return options.requirePrefix .. name
	end

	local tags
	local function lua(ast, forceTag, ...)
		return tags[forceTag or ast.tag](ast, ...)
	end

	tags = setmetatable({
		-- block: { stat* } --
		Block = function(t)
			local r = ""
			for i=1, #t-1, 1 do
				r = r .. lua(t[i]) .. newline()
			end
			if t[#t] then
				r = r .. lua(t[#t])
			end
			return r
		end,

		-- stat --

		-- Do{ stat* }
		Do = function(t)
			return "do" .. indent() .. lua(t, "Block") .. unindent() .. "end"
		end,
		-- Set{ {lhs+} opid? {expr+} }
		Set = function(t)
			if #t == 2 then
				return lua(t[1], "_lhs") .. " = " .. lua(t[2], "_lhs")
			else
				local r = lua(t[1], "_lhs") .. " = " .. lua({ t[2], t[1][1], t[3][1] }, "Op")
				for i=2, math.min(#t[3], #t[1]), 1 do
					r = r .. ", " .. lua({ t[2], t[1][i], t[3][i] }, "Op")
				end
				return r
			end
		end,
		-- While{ expr block }
		While = function(t)
			return "while " .. lua(t[1]) .. " do" .. indent() .. lua(t[2]) .. unindent() .. "end"
		end,
		-- Repeat{ block expr }
		Repeat = function(t)
			return "repeat".. indent() .. lua(t[1]) .. unindent() .. "until " .. lua(t[2])
		end,
		-- If{ (expr block)+ block? }
		If = function(t)
			local r = "if " .. lua(t[1]) .. " then" .. indent() .. lua(t[2]) .. unindent()
			for i=3, #t-1, 2 do
				r = r .. "elseif " .. lua(t[i]) .. " then" .. indent() .. lua(t[i+1]) .. unindent()
			end
			if #t % 2 == 1 then
				r = r .. "else" .. indent() .. lua(t[#t]) .. unindent()
			end
			return r .. "end"
		end,
		-- Fornum{ ident expr expr expr? block }
		Fornum = function(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() .. lua(t[4]) .. unindent() .. "end"
			end
		end,
		-- Forin{ {ident+} {expr+} block }
		Forin = function(t)
			return "for " .. lua(t[1], "_lhs") .. " in " .. lua(t[2], "_lhs") .. " do" .. indent() .. lua(t[3]) .. unindent() .. "end"
		end,
		-- Local{ {ident+} {expr+}? }
		Local = function(t)
			local r = "local "..lua(t[1], "_lhs")
			if t[2][1] then
				r = r .. " = "..lua(t[2], "_lhs")
			end
			return r
		end,
		-- Localrec{ ident expr }
		Localrec = function(t)
			return "local function "..lua(t[1][1])..lua(t[2][1], "_functionWithoutKeyword")
		end,
		-- Goto{ <string> }
		Goto = function(t)
			return "goto " .. lua(t[1], "Id")
		end,
		-- Label{ <string> }
		Label = function(t)
			return "::" .. lua(t[1], "Id") .. "::"
		end,
		-- Return{ <expr*> }
		Return = function(t)
			return "return "..lua(t, "_lhs")
		end,
		-- Break
		Break = function()
			return "break"
		end,
		-- apply (below)

		-- expr --

		-- Nil
		Nil = function()
			return "nil"
		end,
		-- Dots
		Dots = function()
			return "..."
		end,
		-- Boolean{ <boolean> }
		Boolean = function(t)
			return tostring(t[1])
		end,
		-- Number{ <number> }
		Number = function(t)
			return tostring(t[1])
		end,
		-- String{ <string> }
		String = function(t)
			return ("%q"):format(t[1])
		end,
		-- Function{ { ( `ParPair{ Id expr } | `Id{ <string> } )* `Dots? } block }
		_functionWithoutKeyword = function(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 = r .. id
				else
					r = 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 = r .. ", " ..id
					else
						r = r .. ", " .. lua(t[1][i])
					end
				end
			end
			r = r .. ")" .. indent()
			for _, d in ipairs(decl) do
				r = r .. d .. newline()
			end
			return r .. lua(t[2]) .. unindent() .. "end"
		end,
		Function = function(t)
			return "function" .. lua(t, "_functionWithoutKeyword")
		end,
		-- Table{ ( `Pair{ expr expr } | expr )* }
		Pair = function(t)
			return "[" .. lua(t[1]) .. "] = " .. lua(t[2])
		end,
		Table = function(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 = function(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 = function(t)
			return "(" .. lua(t[1]) .. ")"
		end,
		-- apply (below)
		-- lhs (below)

		-- apply --

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

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

		-- lhs --
		_lhs = function(t, start)
			start = start or 1
			local r
			if t[start] then
				r = lua(t[start])
				for i=start+1, #t, 1 do
					r = r .. ", "..lua(t[i])
				end
			else
				r = ""
			end
			return r
		end,
		-- Id{ <string> }
		Id = function(t)
			return t[1]
		end,
		-- Index{ expr expr }
		Index = function(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 = function(self, key)
			error("don't know how to compile a "..tostring(key).." to Lua 5.3")
		end
	})

	#placeholder("patch")

	if opts then
		for k, v in pairs(opts) do
			options[k] = v
		end
	end

	local r = lua(ast)
	return requireStr .. r
end