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--- lam.read
local read = {}
local utf8 = require "utf8"
table.unpack = table.unpack or unpack
local string_to_table =
function(str)
local tbl = {}
for p, c in utf8.codes(str) do
table.insert(tbl, c)
end
return tbl
end
local bslash = { -- backslash characters
a = "\a",
b = "\b",
t = "\t",
n = "\n",
r = "\r",
["\""] = "\"",
["\\"] = "\\",
["|"] = "|",
-- TODO: whitespace
-- \<intraline whitespace>*<line ending> <intraline whitespace>* :
-- nothing
x = -- \x<hex scalar value>; : specified character
function (chars)
local u8ch = {}
repeat
local c = util.pop(chars)
table.insert(u8ch,c)
until c == ";"
table.remove(u8ch) -- remove semicolon
return
utf8.char(tonumber(table.concat(u8ch), 16)),
chars
end,
}
local consume_string =
function(chars)
local str = {}
repeat
local c = util.pop(chars)
if c == "\\" then
c = util.pop(chars)
if bslash[c] then
if type(bslash[c]) == "function" then
c, chars = bslash[c](chars)
table.insert(str, c)
else
table.insert(str, bslash[c])
end
else
table.insert(str, "\\"..c)
end
elseif c == "\"" then
break
else
table.insert(str, c)
end
until #chars == 0
return table.concat(str), chars
end
read.tokenize =
function (program)
if not program or program == "" then return nil end
local tokens = {}
local token = ""
local token_type = nil
local push_token =
function (type, tok)
type = type or token_type
token = tok or token
if token:len() > 0 then
table.insert(tokens, {
type = type,
value = token, })
token = ""
token_type = nil
end
end
local chars = string_to_table(program)
while #chars > 0 do
local c = util.pop(chars)
if c == "(" then
push_token()
push_token("begin_list", "(")
elseif c == ")" then
push_token()
push_token("end_list", ")")
elseif c:match("%s") then -- whitespace
push_token()
elseif c == "\"" then -- string
str, chars = consume_string(chars)
push_token("string", str)
elseif c:match("%d") then -- numbers
token = token .. c
token_type = token_type or "number"
else
token = token .. c
token_type = token_type or "symbol"
end
end
push_token()
return tokens
end
read.tokentable = {
string =
function (tok)
return tok.value
end,
number =
function (tok)
return tonumber(tok.value)
end,
symbol =
function (tok) -- TODO need to return a Symbol from types...
return tok.value
end,
}
read.parse =
function (tokens)
assert(next(tokens), "Unexpected EOF")
tok = util.pop(tokens)
if tok.value == "(" then
local L = {}
while tokens[1].value ~= ")" do
table.insert(L, read.parse(tokens))
end
util.pop(tokens) -- remove ")"
return L
elseif tok.value == ")" then
error("Unexpected ')'")
elseif read.tokentable[tok.type] then
return read.tokentable[tok.type](tok)
else
error("Bad token: '" .. tok.value .. "'")
end
end
read.read = function (program) return read.parse(read.tokenize(program)) end
---
return setmetatable(read, { __call =
function(_, program)
return read.read(program)
end,
})
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