1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
|
--- 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,
}
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
--------
return m
|
