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|
--- lam.read
local m = {}
local t = require "type"
local utf8 = require "utf8"
local pop = require("util").pop
-- TODO:
-- - string reading
-- - # syntax
-- - comments
-- - probably more
function m.inport (source, kind)
-- KIND can be one of "file", "string"; defaults to "file"
-- SOURCE is the name of the file or the string to read, or nil; if nil,
-- read from standard input.
local f, l
local k = kind or "file"
if source then
if kind == "file" then
f = io.open(source, "r")
elseif kind == "string" then
l = m.tochars(source)
end
else
-- KIND is ignored here
f = io.input()
end
local t = {
file = f,
line = l or {},
next_token =
function (self)
local tok, toktype
while true do
if #self.line == 0 and self.file then
self.line = m.tochars(
self.file:read("*l"))
end
if not self.line or #self.line == 0 then
return nil
end
tok, toktype, self.line =
m.scan(self.line)()
if tok then return tok, toktype end
end
end,
}
if t.file then t.close = function (self) self.file:close() end; end
local mt = {
__type = "port",
__tostring =
function (self)
return string.format("#<port %s>",
self.file or "(string)")
end,
}
return setmetatable(t, mt)
end
function m.tochars (s)
local chars = {}
for _, code in utf8.codes(s) do
table.insert(chars, code)
end
return chars
end
--- Consumers
-- These take a table of characters (cs) and return a token and the rest of the
-- chars
local function consume_token (cs)
local token = {}
while #cs > 0 and cs[1]:match("[^%s()\"#'`,@;]") do
table.insert(token, pop(cs))
end
return table.concat(token), cs
end
local function consume_whitespace (cs)
while #cs > 0 and cs[1]:match("%s") do pop(cs) end
return nil, cs
end
--- Reading from a port
m.readtable = {
["("] = function (cs) return pop(cs), "open", cs end,
[")"] = function (cs) return pop(cs), "close", cs end,
["'"] = function (cs) return pop(cs), "quote", cs end,
["`"] = function (cs) return pop(cs), "quote", cs end,
[","] =
function (cs)
pop(cs) -- remove ','
if cs[1] == "@" then
pop(cs) -- remove '@'
return ",@", "quote", cs
else
return ",", "quote", cs
end
end,
}
-- Return an iterator over a character table, so you can do:
-- for token, chars in scan(cs) do ... end
function m.scan (cs)
local cs = cs
return function ()
if not next(cs) then return nil end
local token, toktype
while true do
if m.readtable[cs[1]] then
token, toktype, cs = m.readtable[cs[1]](cs)
return token, toktype, cs
elseif cs[1]:match("%s") then
_, cs = consume_whitespace(cs)
return nil, nil, cs
-- return nil, cs
elseif cs[1]:match("[%d.+-]") then
-- numbers, +, -, ., ...
local token, cs = consume_token(cs)
if token:match("[-+]") or token == "..." then
return token, "symbol", cs
elseif token == "." then
return token, "dot", cs
else
local n = tonumber(token)
assert (n ~= nil, "Bad number: "..n)
return n, "number", cs
end
else
token, cs = consume_token(cs)
return token, "symbol", cs
end
end
end
end
function m.readchar (port)
if #port.line > 0 then
local ch = pop(port.line)
return ch
else
return port.file.read(1)
end
end
m.readmacros = {
quote =
function (tok, toktype, port)
local qs = {
["'"] = "quote",
["`"] = "quasiquote",
[","] = "unquote",
[",@"] = "unquote-splicing",
}
if not qs[tok] then
error(string.format("Bad quote: '%s'\n", tok))
end
local Q = {qs[tok]}
table.insert(Q, m.read(port))
return t.list(Q)
end,
}
function m.read (port)
local function read_ahead (tok, toktype)
if not tok then error("Unexpected EOF") end
if toktype == "open" then
local L = {}
while true do
local tok, toktype = port:next_token()
if toktype == "close" then
return t.list(L)
elseif toktype == "dot" then
local fin = m.read(port)
port:next_token() -- throw away ')'
return t.list(L, fin)
else
table.insert(L,
read_ahead(tok, toktype))
end
end
elseif toktype == "close" then
error("Unexpected ')'")
elseif m.readmacros[toktype] then
return m.readmacros[toktype](tok, toktype, port)
else return tok
end
end
-- body of read
local tok1, toktype1 = port:next_token()
if not tok1 then return nil
else return read_ahead(tok1, toktype1)
end
end
function m.read_string (str)
return m.read(m.inport(str, "string"))
end
---
return m
|
