Im trying to get the value of a map by running Code.eval_string/1 and it fails with error:
warning: variable "data" does not exist and is being expanded to "data()", please use parentheses to remove the ambiguity or change the variable name
nofile:1
** (CompileError) nofile:1: undefined function data/0
(elixir 1.10.2) lib/code.ex:332: Code.eval_string_with_error_handling/3
main.exs:65: RulesEngine.evaluate_object_by_condition/2
(elixir 1.10.2) lib/enum.ex:1396: Enum."-map/2-lists^map/1-0-"/2
main.exs:17: RulesEngine.evaluate_object_by_condition/2
Code is:
#doc "Evaluate condition"
#default_op "="
def evaluate_object_by_condition(data, condition) do
IO.puts("Evaluando una regla en particular:")
IO.inspect(condition)
IO.inspect(data)
attr = condition.attr
value = condition.value
IO.inspect(attr)
eval_data = Code.eval_string(attr)
op = Map.get(condition, "op", #default_op)
IO.puts("DATA to EVAL")
IO.inspect(eval_data)
# value_type = Map.get(condition, "type")
# Hacer type checking y agregar a value_type
## Falta obtener el valor del objeto
# res = evaluate("=", value, obj.value)
true
end
then I run:
obj = %{
value: 1,
tiene_beca: 1,
tiene_credito: 1
}
condition= %{
attr: "data.tiene_beca",
value: 1
}
RulesEngine.evaluate_object_by_condition(obj, rules_or)
So I'm trying to get the value of data.tiene_beca, and getting that variable name from a string, which would be the correct way of doing that in elixir?
First of all, consider whether you actually need all this flexibility. Code.eval_string runs the code without any checks or restrictions whatsoever, so this potentially opens a security hole in the code. I would do something like this instead:
["data", field_name] = String.split(attr, ".")
field_name = String.to_existing_atom(field_name)
eval_data = data[field_name]
That said, the reason your code isn't working is that Code.eval_string doesn't have access to local variables in the calling function, so you'd need to pass the variable as a binding explicitly:
eval_data = Code.eval_string(attr, [data: data])
Related
local httpService = game :GetService("HttpService")
local laber = script.Parent.SurfaceGui.TextLabel
local URL = "https://api.coingecko.com/api/v3/coins/markets?vs_currency=usd&order=market_cap_desc&per_page=100&page=1&sparkline=false"
local Data = httpService:GetAsync(URL)
local randomJokes = httpService:JSONDecode(Data)
nil.Text = randomJokes.value
Literals can't be used as "prefix expressions" to prefix .name, [exp] for assignments.
The workaround is to wrap literals in parentheses (for example: ("str"):rep(42)).
In your case, you can syntactically fix your code by wrapping nil in parentheses:
(nil).Text = randomJokes.value
which most likely is nonsense semantically, unless someone did
debug.setmetatable(nil, {__newindex = function(_, key, value) ... end})
What did you intend to achieve?
I wrote simple class to compress data. Here it is:
LZWCompressor = {}
function LZWCompressor.new()
local self = {}
self.mDictionary = {}
self.mDictionaryLen = 0
-- ...
self.Encode = function(sInput)
self:InitDictionary(true)
local s = ""
local ch = ""
local len = string.len(sInput)
local result = {}
local dic = self.mDictionary
local temp = 0
for i = 1, len do
ch = string.sub(sInput, i, i)
temp = s..ch
if dic[temp] then
s = temp
else
result[#result + 1] = dic[s]
self.mDictionaryLen = self.mDictionaryLen + 1
dic[temp] = self.mDictionaryLen
s = ch
end
end
result[#result + 1] = dic[s]
return result
end
-- ...
return self
end
And i run it by:
local compressor = LZWCompression.new()
local encodedData = compressor:Encode("I like LZW, but it doesnt want to compress this text.")
print("Input length:",string.len(originalString))
print("Output length:",#encodedData)
local decodedString = compressor:Decode(encodedData)
print(decodedString)
print(originalString == decodedString)
But when i finally run it by lua, it shows that interpreter expected string, not Table. That was strange thing, because I pass argument of type string. To test Lua's logs, i wrote at beggining of function:
print(typeof(sInput))
I got output "Table" and lua's error. So how to fix it? Why lua displays that string (That i have passed) is a table? I use Lua 5.3.
Issue is in definition of method Encode(), and most likely Decode() has same problem.
You create Encode() method using dot syntax: self.Encode = function(sInput),
but then you're calling it with colon syntax: compressor:Encode(data)
When you call Encode() with colon syntax, its first implicit argument will be compressor itself (table from your error), not the data.
To fix it, declare Encode() method with colon syntax: function self:Encode(sInput), or add 'self' as first argument explicitly self.Encode = function(self, sInput)
The code you provided should not run at all.
You define function LZWCompressor.new() but call CLZWCompression.new()
Inside Encode you call self:InitDictionary(true) which has not been defined.
Maybe you did not paste all relevant code here.
The reason for the error you get though is that you call compressor:Encode(sInput) which is equivalent to compressor.Encode(self, sInput). (syntactic sugar) As function parameters are not passed by name but by their position sInput inside Encode is now compressor, not your string.
Your first argument (which happens to be self, a table) is then passed to string.len which expects a string.
So you acutally call string.len(compressor) which of course results in an error.
Please make sure you know how to call and define functions and how to use self properly!
My game engine pushes a value on to the lua stack as a parameter to a function and then invokes it using lua_pcall. The lua code will run and call additional lua functions. Eventually this lua code will invoke a C function. Is it possible for this function to retrieve the value that was originally pushed on to the stack?
Its like this:
<engine function A>
pushes parameter value X on to stack for lua
<lua func>
<lua func>
<lua func>
<engine function B>
can I extract the values X that was pushed by function A here?
Yes, with a combination of getinfo, getlocal and getupvalue you can get all that information (you can even change those values using set* functions).
Here is a fragment from MobDebug that returns stack information along with a table of locals and upvalues at each level. The variables at each level will be indexed in the same order they appear in the code (starting from parameters). For each get* function you can use their C equivalents (lua_getinfo, lua_getlocal, and lua_getupvalue), but the logic should be exactly the same.
local function stack(start)
local function vars(f)
local func = debug.getinfo(f, "f").func
local i = 1
local locals = {}
while true do
local name, value = debug.getlocal(f, i)
if not name then break end
if string.sub(name, 1, 1) ~= '(' then locals[name] = {value, tostring(value)} end
i = i + 1
end
i = 1
local ups = {}
while func and true do -- check for func as it may be nil for tail calls
local name, value = debug.getupvalue(func, i)
if not name then break end
ups[name] = {value, tostring(value)}
i = i + 1
end
return locals, ups
end
local stack = {}
for i = (start or 0), 100 do
local source = debug.getinfo(i, "Snl")
if not source then break end
table.insert(stack, {
{source.name, source.source, source.linedefined,
source.currentline, source.what, source.namewhat, source.short_src},
vars(i+1)})
if source.what == 'main' then break end
end
return stack
end
What I'm currently trying to do is make a table of email addresses (as keys) that hold person_records (as values). Where the person_record holds 6 or so things in it. The problem I'm getting is that when I try to assign the email address as a key to a table it complains and says table index is nil... This is what I have so far:
random_record = split(line, ",")
person_record = {first_name = random_record[1], last_name = random_record[2], email_address = random_record[3], street_address = random_record[4], city = random_record[5], state = random_record[6]}
email_table[person_record.email_address] = person_record
I wrote my own split function that basically takes a line of input and pulls out the 6 comma seperated values and stores them in a table (random_record)
I get an error when I try to say email_table[person_record.email_address] = person_record.
But when I print out person_record.email_address it's NOT nil, it prints out the string I stored in it.. I'm so confused.
function split(str, pat)
local t = {} -- NOTE: use {n = 0} in Lua-5.0
local fpat = "(.-)" .. pat
local last_end = 1
local s, e, cap = str:find(fpat, 1)
while s do
if s ~= 1 or cap ~= "" then
table.insert(t,cap)
end
last_end = e+1
s, e, cap = str:find(fpat, last_end)
end
if last_end <= #str then
cap = str:sub(last_end)
table.insert(t, cap)
end
return t
end
The following code is copy and pasted from your example and runs just fine:
email_table = {}
random_record = {"first", "second", "third"}
person_record = {first_name = random_record[1], last_name = random_record[1], email_address = random_record[1]}
email_table[person_record.email_address] = person_record
So your problem is in your split function.
BTW, Lua doesn't have "hashtables". It simply has "tables" which store key/value pairs. Whether these happen to use hashes or not is an implementation detail.
It looks like you iterating over some lines that have comma-separated data.
Looking at your split function, it stops as soon as there's no more separator (,) symbols in particular line to find. So feeding it anything with less than 3 ,-separated fields (for very common example: an empty line at end of file) will produce a table that doesn't go up to [3]. Addressing any empty table value will return you a nil, so person_record.email_address will be set to nil as well on the 2nd line of your code. Then, when you attempt to use this nil stored in person_record.email_address as an index to email_table in 3rd line, you will get the exact error you've mentioned.
I am starting to learn Lua from Programming in Lua (2nd edition)
I didn't understand the following in the book. Its very vaguely explained.
a.) w={x=0,y=0,label="console"}
b.) x={math.sin(0),math.sin(1),math.sin(2)}
c.) w[1]="another field"
d.) x.f=w
e.) print (w["x"])
f.) print (w[1])
g.) print x.f[1]
When I do print(w[1]) after a.), why doesn't it print x=0
What does c.) do?
What is the difference between e.) and print (w.x)?
What is the role of b.) and g.)?
You have to realize that this:
t = {3, 4, "eggplant"}
is the same as this:
t = {}
t[1] = 3
t[2] = 4
t[3] = "eggplant"
And that this:
t = {x = 0, y = 2}
is the same as this:
t = {}
t["x"] = 0
t["y"] = 2
Or this:
t = {}
t.x = 0
t.y = 2
In Lua, tables are not just lists, they are associative arrays.
When you print w[1], then what really matters is line c.) In fact, w[1] is not defined at all until line c.).
There is no difference between e.) and print (w.x).
b.) creates a new table named x which is separate from w.
d.) places a reference to w inside of x. (NOTE: It does not actually make a copy of w, just a reference. If you've ever worked with pointers, it's similar.)
g.) Can be broken up in two parts. First we get x.f which is just another way to refer to w because of line d.). Then we look up the first element of that table, which is "another field" because of line c.)
There's another way of creating keys in in-line table declarations.
x = {["1st key has spaces!"] = 1}
The advantage here is that you can have keys with spaces and any extended ASCII character.
In fact, a key can be literally anything, even an instanced object.
function Example()
--example function
end
x = {[Example] = "A function."}
Any variable or value or data can go into the square brackets to work as a key. The same goes with the value.
Practically, this can replace features like the in keyword in python, as you can index the table by values to check if they are there.
Getting a value at an undefined part of the table will not cause an error. It will just give you nil. The same goes for using undefined variables.
local w = {
--[1] = "another field"; -- will be set this value
--["1"] = nil; -- not save to this place, different with some other language
x = 0;
y = 0;
label = "console";
}
local x = {
math.sin(0);
math.sin(1);
math.sin(2);
}
w[1] = "another field" --
x.f = w
print (w["x"])
-- because x.f = w
-- x.f and w point one talbe address
-- so value of (x.f)[1] and w[1] and x.f[1] is equal
print (w[1])
print ((x.f)[1])
print (x.f[1])
-- print (x.f)[1] this not follows lua syntax
-- only a function's has one param and type of is a string
-- you can use print "xxxx"
-- so you print x.f[1] will occuur error
-- in table you can use any lua internal type 's value to be a key
-- just like
local t_key = {v=123}
local f_key = function () print("f123") end
local t = {}
t[t_key] = 1
t[f_key] = 2
-- then t' key actualy like use t_key/f_key 's handle
-- when you user t[{}] = 123,
-- value 123 related to this no name table {} 's handle