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|
--- lam.read
local read = {}
local type = require "type"
local utf8 = require "utf8"
local util = require "util"
local pop = util.pop
local unpack = table.unpack or unpack
local function program_characters (program)
local chars = {}
for pos, code in utf8.codes(program) do
table.insert(chars, code)
end
return chars
end
local function consume_string_whitespace (chars)
-- \<intraline ws>*<line ending> <intraline ws>* : nothing
local s = {"\\"}
while chars[1]:match("[ \t]") do
table.insert(s, pop(chars))
end
if chars[1] ~= "\n" then
table.insert(s, chars[1])
return table.concat(s), chars
end
while chars[1]:match("%s") do
pop(chars)
end
return chars[1], chars
end
local function consume_string_hexvalue (chars)
-- \x<hex scalar value>; : specified character
local u8ch = {}
repeat
local c = pop(chars)
table.insert(u8ch, c)
until c == ";"
table.remove(u8ch) -- remove semicolon
return utf8.char(tonumber(table.concat(u8ch), 16)), chars
end
local function consume_string (chars)
local str = {}
local backslash = {
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(chars) -- throw initial " away
repeat
local c = pop(chars)
if c == [[\]] then
c = chars[1]
if backlash[c] then
if type(backslash[c]) == "function" then
c, chars = backslash[c](chars)
table.insert(str, c)
else
table.insert(str, backlash[c])
end
else
table.insert(str, "\\"..c)
end
pop(chars)
elseif c == [["]] then
break
else
table.insert(str, c)
end
until #chars == 0
return table.concat(str), "string", chars
end
local function consume_token (chars)
local tok = {}
while #chars>0 and chars[1]:match("[^%s()\"#'`,@;]") do
table.insert(tok, pop(chars))
end
return table.concat(tok), chars
end
local consume_symbol = consume_token
local function consume_number (chars)
local digits, chars = consume_token(chars)
local num = tonumber(digits)
if num == nil then error("Bad number: " .. num) end
return num, chars
end
local function consume_whitespace (chars)
while #chars>0 and chars[1]:match("%s") do pop(chars) end
return chars
end
local function consume_comment (chars)
local comment = {}
repeat
table.insert(comment, pop(chars))
until #chars == 0 or chars[1]:match("\n")
return table.concat(comment), "comment", chars
end
--- API
read.readtable = {
["("] = function(chars) return pop(chars), "open", chars end,
[")"] = function(chars) return pop(chars), "close", chars end,
["'"] = function(chars) return pop(chars), "quote", chars end,
["`"] = function(chars) return pop(chars), "quote", chars end,
[","] = function(chars) return pop(chars), "quote", chars end,
["."] = function(chars) return pop(chars), "dot", chars end,
["\""] = consume_string,
[";"] = consume_comment,
-- ["#"] = ...,
}
function read.scan (chars)
local chars = chars
return function ()
if not next(chars) then return nil end
local token, toktype = "", nil
while true do
if read.readtable[chars[1]] then
token, toktype, chars =
read.readtable[chars[1]](chars)
return token, toktype
elseif chars[1]:match("%s") then
chars = consume_whitespace(chars)
elseif chars[1]:match("[%d-]") then
token, chars = consume_number(chars)
return token, "number"
else
token, chars = consume_symbol(chars)
return token, "symbol"
end
if #chars == 0 then return nil end
end
end
end
function read.tokenize (program)
if not program or #program == 0 then return nil end
local tokens = {}
for token, toktype in read.scan(program_characters(program)) do
table.insert(tokens, {type = toktype, value = token})
end
return tokens
end
read.readmacros = {
open =
function (token, tokens)
local L, lt = {}, nil
while tokens[1].type ~= "close" do
local nt = read.parse(tokens)
-- this isn't .. my /favorite/ implementation,
-- but it works
if nt == "." then
lt = read.parse(tokens)
break
else
table.insert(L, nt)
end
assert(tokens[1], "Unexpected EOF")
end
pop(tokens) -- remove final ")"
return type.List(L, lt)
end,
close =
function (token, tokens)
error ("Unexpected '" .. token.value .. "'")
end,
quote =
function (token, tokens)
local Q
if token.value == "'" then
Q = {"quote"}
elseif token.value == "`" then
Q = {"quasiquote"}
elseif token.value == "," then
Q = {"unquote"}
end
table.insert(Q, read.parse(tokens))
return type.List(Q)
end,
}
function read.parse (tokens)
if not next(tokens) then return nil end
local token = pop(tokens)
if read.readmacros[token.type] then
return read.readmacros[token.type](token, tokens)
else
return token.value
end
end
function read.read (program)
return read.parse(read.tokenize(program))
end
---
return read
|
