path: root/read.lua

--- lam.read

local m = {}
local type = require("type")
local eof, input_port = type.eof, type.input_port
local util = require("util")
local error, pop = util.error, util.pop
local utf8_char = require("utf8").char

local token_separators = "[%s#()\"'`,@;]"

local function consume_token (cs)
	local tok = {}
	while #cs > 0 and not cs[1]:match(token_separators) do
		local c = pop(cs)
		table.insert(tok, c)
	end
	return table.concat(tok), cs
end

---[[ READ TABLE ]]---

--- helper functions

local function consume_unquote (cs)
	pop(cs) -- remove ','
	if cs[1] == "@" then
		pop(cs) -- remove '@'
		return ",@", "quote", cs
	else
		return ",", "quote", cs
	end
end

local function consume_comment (cs)
	local comment = {}
	while #cs > 0 and not cs[1]:match("\n") do
		table.insert(comment, pop(cs))
	end
	return table.concat(comment), "comment", cs
end

local function consume_literal (cs)
	local tok

	-- read '#\ ' and such correctly
	if cs[2] == "\\" then
		if not cs[3] then error("bad literal", "#\\") end
		if cs[3]:match(token_separators) then
			pop(cs) -- remove '\'
			pop(cs) -- remove next character
			return type.character(cs[1])
		end
	end

	pop(cs) -- discard '#' ...
	tok, cs = consume_token(cs)
	tok = "#" .. tok -- ... then put it back

	print(tok)

	local val
	if m.readtable.literals.lit[tok] ~= nil then
		val = m.readtable.literals.lit[tok]
	else
		for re, fn in pairs(m.readtable.literals.regex)
		do
			if tok:match(re) then
				val = fn(tok)
			end
		end
	end

	if val == nil then
		error("bad literal", tok)
	end
	return val, "literal", cs
end

local function consume_whitespace (cs)
	while #cs > 0 and cs[1]:match("%s") do
		pop(cs)
	end
	return false, nil, cs
end

local function consume_number_etc (cs)
	-- Since numbers can start with +, -, and ., those symbols and ... are
	-- handled along with numbers.
	local tok
	tok, cs = consume_token(cs)
	if tok:match("^[-+]$") or tok == "..." then
		return tok, "symbol", cs
	elseif tok == "." then
		return tok, "dot", cs
	else -- number
		local n = tonumber(tok)
		if not n then
			error("bad number", n)
		end
		return n, "number", cs
	end
end

-- strings

local function consume_string_whitespace (cs)
	-- \<intraline ws>*<line ending> <intraline ws>* : nothing
	local s = {"\\"}
	while cs[1]:match("[ \t]") do
		table.insert(s, pop(cs))
	end
	if cs[1] ~= "\n" then
		table.insert(s, cs[1])
		return table.concat(s), cs
	end
	while cs[1]:match("%s") do
		pop(cs)
	end
	return cs[1], cs
end

local function consume_string_hexvalue (cs)
	-- \x<hex scalar value>; : specified character
	local u8ch = {}
	repeat
		local c = pop(cs)
		table.insert(u8ch, c)
	until c == ";"
	table.remove(u8ch) -- discard ';'
	return utf8_char(tonumber(table.concat(u8ch), 16)), cs
end

local function consume_string (cs)
	local str = {}
	local escapes = {
		a = "\a",
		b = "\b",
		t = "\t",
		n = "\n",
		r = "\r",
		["\""] = "\"",
		["\\"] = "\\",
		["|"] = "|",
		[" "] = consume_string_whitespace,
		["\t"] = consume_string_whitespace,
		["\n"] = consume_string_whitespace,
		x = consume_string_hexvalue,
	}
	pop(cs) -- discard '"'
	repeat
		local c = pop(cs)
		if c == "\\" then
			c = cs[1]
			if escapes[c] then
				if type.luatype(escapes[c]) == "function" then
					c, cs = escapes[c](cs)
					table.insert(str, c)
				else
					table.insert(str, escapes[c])
				end
			else
				table.insert(str, "\\"..c)
			end
			pop(cs)
		elseif c == "\"" then
			break
		else
			table.insert(str, c)
		end
	until #cs == 0
	return type.string(str), "string", cs
end

local function consume_char_as (token_type)
	-- return a function that pops a character and returns it with
	-- TOKEN_TYPE
	return function (cs) return pop(cs), token_type, cs end
end

-- each function should take a list of characters and return the token, its
-- type, and the rest of the characters
m.readtable = {}
m.readtable.chars = {
	["("] = consume_char_as("open"),
	[")"] = consume_char_as("close"),
	["'"] = consume_char_as("quote"),
	["`"] = consume_char_as("quote"),
	[","] = consume_unquote,
	["\""] = consume_string,
	[";"] = consume_comment,
	["#"] = consume_literal,
}
m.readtable.regex = {
	["%s"] = consume_whitespace,
	["[%d.+-]"] = consume_number_etc,
}
m.readtable.default = -- default action if nothing else matches
	function (cs)
		local tok, cs = consume_token(cs)
		return tok, "symbol", cs
	end

-- convenience function to make writing the regexen rules easier below
local function based_num (base)
	return function (token)
		local n = tonumber(token:sub(3), base)
		if not n then
			error("bad number", token)
		end
		return n
	end
end

m.readtable.literals = {
	lit = {
		["#t"] = true,
		["#true"] = true,
		["#f"] = false,
		["#false"] = false,
	},
	regex = {
		["^#b"] = based_num(2),
		["^#o"] = based_num(8),
		["^#d"] = based_num(10),
		["^#x"] = based_num(16),
		["^#\\."] =
			function (tok)
				return type.character(tok:sub(3))
			end,
	},
}
-- add named characters
for char, name in pairs(type.character_names) do
	m.readtable.literals.lit["#\\"..name] = type.character(char)
end

---[[ READER MACROS ]]---
-- Each of these are named after the type of the token read and contain
-- function taking (TOKEN, TYPE, PORT) and returning a lisp object

m.readmacros = {
	close =
		function (token, _, _)
			error("unexpected", token)
		end,
	quote =
		function (token, _, port)
			local qs = {
				["'"] = "quote",
				["`"] = "quasiquote",
				[","] = "unquote",
				[",@"] = "unquote-splicing",
			}
			if not qs[token] then
				error("bad quote", token)
			end
			local Q = {qs[token]}
			table.insert(Q, m.read(port))
			return type.list(Q)
		end,
	comment = function (_,_,_) return nil end,
}

---[[ READ ]]---

function m.read (port)
	local function read_ahead(token, token_type)
		if token == eof then error("unexpected", token) end
		if token_type == "open" then
			-- this must be defined here because it calls read_ahead
			-- recursively.
			local L = {}
			repeat
				token, token_type = port:next(m.readtable)
				if token_type == "close" then
					return type.list(L)
				elseif token_type == "dot" then
					local fin = m.read(port)
					port:next(m.readtable) -- discard ')'
					return type.list(L, fin)
				else
					table.insert(L,
						read_ahead(token, token_type))
				end
			until nil
		elseif m.readmacros[token_type] then
			return m.readmacros[token_type](token, token_type, port)
		else
			return token
		end
	end
	---
	local token1, type1 = port:next(m.readtable)
	if token1 == eof then
		return eof
	else
		return read_ahead(token1, type1)
	end
end

function m.read_string (str)
	return m.read(input_port(str, "string"))
end

--------
return m