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|
--- lam.type
local m = {}
local utf8 = require "utf8"
utf_char, utf_codepoint = utf8.char, utf8.codepoint
--- atomic types
-- true, false and nil are just ... true, false, and nil
-- Characters contain both their string reputations and their codepoints
function m.character (x)
-- is storing a character with its string and numerical representation
-- overkill? ... maybe.
local s = tostring(x)
local uc = utf_codepoint(s)
local t = { -- String representation of the character
v = utf_char(uc),
u = uc,
}
local mt = {
__type = "character",
__eq = function (self) return self.v end,
__lt = function (a, b) return a.u < b.u end,
__tostring =
function (self)
local v = self.v
if v == "\n" then
return "#\\newline"
elseif v == " " then
return "#\\space"
else
return "#\\" .. v
end
end,
}
return setmetatable(t, mt)
end
-- a symbol is just a string, unadorned. I was going to have a character be
-- represented by a one-character string, but then it would be indistinguishable
-- from a one-character symbol internally.
m.symbol = tostring
-- for now, number will just be lua's number. At *some* point, it will be the
-- whole numeric tower, yaaayyy
m.number = tonumber
-- strings are wrapped strings
function m.string (x)
local x = tostring(x)
local t = {
v = x,
escape =
function (self)
return self.v:gsub("[\\\"]", "\\%1")
end,
}
local mt = {
__type = "string",
__tostring =
function (self)
return "\"" .. self:escape() .. "\""
end,
}
return setmetatable(t, mt)
end
-- null () is both an atom and a list (yay)
-- this one is NOT a function
m.null = setmetatable({}, {
__type = "null",
__tostring = function (self) return "()" end,
})
--- collection types
-- cons are lisp's fundamental collection type
function m.cons (a, b)
local t = { a, b, }
local mt = {
__type = "cons",
__tostring =
function (self)
local out = {}
local car, cdr = self[1], self[2]
while cdr do
table.insert(out, tostring(car))
if m.luatype(cdr) == "table" then
car = cdr[1]
cdr = cdr[2]
else
table.insert(out, ".")
table.insert(out, cdr)
break
end
end
return "(" .. table.concat(out, " ") .. ")"
end,
__len =
function (self)
local function go (lis, acc)
-- improper lists don't have lengths
-- ... but don't error here.
if not m.isa(lis, "cons") then
return nil
end
if lis[2] == m.null then return acc
else return go(lis[2], acc+1)
end
end
return go(self, 1)
end,
}
return setmetatable(t, mt)
end
-- lists are singly-linked cons cells
function m.list (items, last)
-- ITEMS is a table and LAST is an optional final cdr. If it's nil, the
-- list is a "proper" list; that is, it ends in ().
local function tolist (base, items)
if #items == 0 then return base end
return tolist(m.cons(table.remove(items), base), items)
end
return tolist(last or m.null, items)
end
-- convert a list to a lua table
function m.totable (cons)
local t = {}
local car, cdr = cons[1], cons[2]
while cdr do
table.insert(t, car)
if m.luatype(cdr) == "table" then
car = cdr[1]
cdr = cdr[2]
else
table.insert(t, cdr)
end
end
return t
end
-- testing types
-- we love name collisions
m.luatype = type
function m.lamtype (x)
if m.luatype(x) == "string" then
return "symbol"
elseif getmetatable(x) and getmetatable(x).__type then
return getmetatable(x).__type
else
return m.luatype(x)
end
end
function m.isa (x, t)
return m.lamtype(x) == t
end
function m.islist (x)
-- TODO: detect circular lists
if x == m.null then
return true
elseif m.isa(x, "cons") then
return m.islist(x[2])
else
return false
end
end
function m.isatom (x)
if x == m.null then
return true -- '() is the only value that is both atom and list
elseif m.luatype(x) == "table" then
-- generally, anything that's implemented as a table is *not* an
-- atom, at least as I will define it. (it's not an actual
-- scheme procedure)
return false
else
return true
end
end
--------
return m
|
