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
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
|
--[[--------------------------------------------------------------------
sample_expr.lua
Stand-alone expression parsing demonstrator.
This file is part of Yueliang.
Copyright (c) 2005 Kein-Hong Man <khman@users.sf.net>
The COPYRIGHT file describes the conditions
under which this software may be distributed.
See the ChangeLog for more information.
----------------------------------------------------------------------]]
--[[--------------------------------------------------------------------
-- Notes:
-- * this is an interactive demonstrator for implementing expression
-- parsing in ChunkBake, a Lua assembler
-- * evaluation is immediate, and a result is immediately generated
----------------------------------------------------------------------]]
require("../lzio.lua")
require("../llex.lua")
luaX:init()
------------------------------------------------------------------------
-- expression parser
------------------------------------------------------------------------
expr = {}
expr.unop = {
["TK_NOT"] = true,
["-"] = true,
}
expr.binop = {
["^"] = 10,
["*"] = 7,
["/"] = 7,
["+"] = 6,
["-"] = 6,
["TK_CONCAT"] = 5,
["TK_NE"] = 3,
["TK_EQ"] = 3,
["<"] = 3,
["TK_LE"] = 3,
[">"] = 3,
["TK_GE"] = 3,
["TK_AND"] = 2,
["TK_OR"] = 1,
}
expr.binop_r = {
["^"] = 9,
["*"] = 7,
["/"] = 7,
["+"] = 6,
["-"] = 6,
["TK_CONCAT"] = 4,
["TK_NE"] = 3,
["TK_EQ"] = 3,
["<"] = 3,
["TK_LE"] = 3,
[">"] = 3,
["TK_GE"] = 3,
["TK_AND"] = 2,
["TK_OR"] = 1,
}
function expr:parse(str)
self.LS = {}
self.L = {}
self.z = luaZ:init(luaZ:make_getS(str), nil, "=string")
luaX:setinput(self.L, self.LS, self.z, self.z.name)
self:token()
local v = self:expr()
if self.tok ~= "TK_EOS" then
io.stderr:write("parse error: some tokens unparsed\n")
end
return v
end
function expr:token()
self.tok = luaX:lex(self.LS, self.LS.t)
self.seminfo = self.LS.t.seminfo
return self.tok
end
function expr:simpleexpr()
local tok = self.tok
if tok == "TK_NIL" then
self:token()
return nil
elseif tok == "TK_TRUE" then
self:token()
return true
elseif tok == "TK_FALSE" then
self:token()
return false
elseif tok == "TK_NUMBER" or tok == "TK_STRING" then
self:token()
return self.seminfo
elseif tok == "(" then
self:token()
local v = self:expr()
if self.tok ~= ")" then
io.stderr:write("parse error: expecting ')' to delimit\n")
else
self:token()
return v
end
end
self:token()
io.stderr:write("parse error: "..tok.." encountered, substituting nil\n")
return nil
end
function expr:subexpr(prev_op)
local v, op
if self.unop[self.tok] then
op = self.tok
self:token()
v = self:subexpr(8)
if op == "TK_NOT" then
v = not v
else-- op == "-" then
v = -v
end
else
v = self:simpleexpr()
end
op = self.tok
if self.binop[op] then
while self.binop[op] and self.binop[op] > prev_op do
self:token()
local v2, next_op = self:subexpr(self.binop_r[op])
if op == "^" then
v = v ^ v2
elseif op == "*" then
v = v * v2
elseif op == "/" then
v = v / v2
elseif op == "+" then
v = v + v2
elseif op == "-" then
v = v - v2
elseif op == "TK_CONCAT" then
v = v .. v2
elseif op == "TK_NE" then
v = v ~= v2
elseif op == "TK_EQ" then
v = v == v2
elseif op == "<" then
v = v < v2
elseif op == "TK_LE" then
v = v <= v2
elseif op == ">" then
v = v > v2
elseif op == "TK_GE" then
v = v >= v2
elseif op == "TK_AND" then
v = v and v2
else-- op == "TK_OR" then
v = v or v2
end
op = next_op
end
end
return v, op
end
function expr:expr()
return self:subexpr(-1)
end
------------------------------------------------------------------------
-- interactive test code
------------------------------------------------------------------------
io.stdout:write([[
Lua-style expression parsing demonstrator.
Type 'exit' or 'quit' at the prompt to terminate session.
]])
local done = false
while not done do
io.stdout:write(":>")
io.stdout:flush()
local l = io.stdin:read("*l")
if l == nil or (l == "exit" or l == "quit" and not prevline) then
done = true
else
local v = tostring(expr:parse(l))
io.stdout:write(v, "\n")
end
end--while
--end
|
