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|
--- lam.read
local m = {}
local type = require("type")
local port = require("port")
local eof, input_port = port.eof, port.input_port
local util = require("util")
local constantly, error, pop = util.constantly, util.error, util.pop
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 ]]---
-- 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 = {
["("] = 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,
[","] = -- unquote
function (cs)
pop(cs) -- remove ','
if cs[1] == "@" then
pop(cs) -- remove '@'
return ",@", "quote", cs
else
return ",", "quote", cs
end
end,
[";"] = -- comment
function (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,
["#"] = -- literal
function (cs)
local tok
-- bail on just '#\'
if not (cs[2] and cs[3]) then
cs = {}
error("bad literal", "#\\")
end
-- read '#\ ' and such correctly
if cs[2] == "\\" and cs[3]:match(token_separators) then
pop(cs) -- remove '\'
pop(cs) -- remove next character
return type.character(cs[1])
end
pop(cs) -- discard '#' ...
tok, cs = consume_token(cs)
tok = "#" .. tok -- ... then put it back
local val
if m.readtable.literals.lit[tok] 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,
}
m.readtable.regex = {
["%s"] = -- whitespace
function (cs)
while #cs > 0 and cs[1]:match("%s") do
pop(cs)
end
return false, nil, cs
end,
["[%d.+-]"] = -- numbers and symbols +, -, ., and ...
function (cs)
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,
}
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 = constantly(nil), -- throw comments away
}
---[[ 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
|
