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--[[--------------------------------------------------------------------
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
|