I'm looking to iterate over some similarly named variables. a_1,a_2,a_3=1,2,3
So that instead of using:
if a_1>0 then a_1-=1 end
if a_2>0 then a_2-=1 end
if a_3>0 then a_3-=1 end
I can do something like:
for i=1,3 do
if a_'i'>1 then a_'i'-=1 end --syntax is wrong here
end
Not sure how to go about doing this, as stated there is no access to _G library in pico8. var-=1 is just var=var-1. Given there are functions like tostr() and tonum() was wondering if there was a tovar() kind of trick to this. Basically need a way to convert the i value to a letter in my variable name and concat it to the variable name...in the conditional statement. Or some alternative method if there is one.
In Lua, when in doubt, use a table.
In this case you could put the 3 variable on a table at the start, and unpack them at the end:
local a={a_1,a_2,a_3}
for i=1,3 do
if(a[i]>1) a[i]-=1
end
a_1,a_2,a_3=unpack(a)
Not sure which Lua version does pico 8 use but for LuaJIT, you could try using loadstring and there is load for Lua5.2+ (I know, not the best solution):
for i = 1, 3 do
local x
loadstring("x = a_" .. tostring(i))()
if x > 1 then
x = x - 1
loadstring("a_" .. tostring(i) .. " = x")()
end
end
Related
I have actually been wondering about this question for a long time, and I can recall reading something somewhere on the internet about loading all local variables into a table, but I could never find it again.
What I am wondering is if there is basically any way to dynamically create a local variable, similar to how you can dynamically create a global variable.
In Lua you can create dynamic global variables simply by saying:
local my_env = getfenv(1);
for i = 1, 10 do
my_env["OMG_DYNAMIC_GLOBAL_VARIABLE_"..i] = i * i;
end
But I have always wondered if there is a way to essentially do the same or a similar thing for local variables. Something like
for i = 1, 10 do
local["OMG_DYNAMIC_LOCAL_VARIABLE_"..i] = i * i;
end
would kind of be pseudo code for what I am trying to do.
As a second part to my question, I am wondering if there is any way to possibly iterate through every local variable in the current scope? I guess pseudo code for what I am trying to do would look something like:
local a = 123;
local b = 321;
LocalVars = {(local)}; --the table with the local variables in it.
for i,v in pairs(LocalVars) do print(i, v); end
I would appreciate any help regarding either part of my question.
Thanks
the table with the local variables in it
There is no table with local variables. Local variables do not exist in compiled Lua. There are simply locations on the Lua stack and/or upvalues. Even the names of local variables are lost during the compilation process.
Local variables are always static constructs of the Lua source code. They never exist within a table. If you need a non-static construct, use a table. That's what tables are for. That's (part of) why Lua globals are in a table.
I don't see the advantage of what you proposed over a regular local table except for syntactic sugar.
local locals = {}
locals.a = 123
locals.b = 321
for i,v in pairs(locals) do
print(i, v)
end
The syntax you proposed does not make the program clearer or easier to read in any way. In fact it even creates new problems. Does the following print c as well or does it not because it is in a nested local scope?
for i,v in pairs(LocalVars) do
local c = 1729
print(i, v)
end
I want to know how to get the table hex id. I know that doing:
local some_var = {}
print (some_var)
the result is (for instance):
table: 0x21581c0
I want the hex without the table: string. I know that maybe some of you suggest me to make a regular expression (or something similar) to remove those chars, but I want to avoid that, and just get the 0x21581c0
Thanks
This is simpler and works for all types that are associated with pointers:
local function getId(t)
return string.format("%p", t)
end
print("string:", getId("hi"))
print("table:", getId({}))
print("userdata:", getId(io.stdin))
print("function:", getId(print))
print("number:", getId(1))
print("boolean:", getId(false))
print("nil:", getId(nil))
Result:
string: 0x0109f04638
table: 0x0109f0a270
userdata: 0x01098076c8
function: 0x0109806018
number: NULL
boolean: NULL
nil: NULL
In the standard implementation, there is the global 'print' variable that refers to a standard function that calls, through the global variable 'tostring', a standard function described here. The stanard 'tostring' function is the only way to retrieve the hexadecimal number it shows for a table.
Unfortunately, there is no configuration for either of the functions to do anything differently for all tables.
Nonetheless, there are several points for modification. You can create you own function and call that every time instead, or point either of the the global variables print or tostring to you own functions. Or, set a __tostring metamethod on each table you need tostring to return a different answer for. The advantage to this is it gets you the format you want with only one setup step. The disadvantage is that you have to set up each table.
local function simplifyTableToString(t)
local answer = tostring(t):gsub("table: ", "", 1)
local mt = getmetatable(t)
if not mt then
mt = {}
setmetatable(t, mt)
end
mt.__tostring = function() return answer end
end
local a = {}
local b = {}
print(a, b)
simplifyTableToString(a)
print(a, b)
Without complex patterns, you can just search for the first space, and grab the substring of what follows.
function get_mem_addr (object)
local str = tostring(object)
return str:sub(str:find(' ') + 1)
end
print(get_mem_addr({})) -- 0x109638
print(get_mem_addr(function () end)) -- 0x108cf8
This function will work with tables and functions, but expect errors if you pass it anything else.
Or you can use a little type checking:
function get_mem_addr (o)
return tostring(o):sub(type(o):len() + 3)
end
The table id stated by the OP is invalid in the version of Lua I am using (5.1 in Roblox). A valid ID is length 8, not 9 as in your example. Either way, just use string.sub to get the sub-string you are after.
string.sub(tostring({}), 8)
The reason is, 'table: ' is 7 characters long, so we take from index 8 through the end of the string which returns the hex value.
I need this for a game server using Lua..
I would like to be able to save all combinations of a name
into a string that can then be used with:
if exists (string)
example:
ABC_-123
aBC_-123
AbC_-123
ABc_-123
abC_-123
etc
in the game only numbers, letters and _ - . can be used as names.
(A_B-C, A-B.C, AB_8 ... etc)
I understand the logic I just don't know how to code it:D
0-Lower
1-Upper
then
000
001
etc
You can use recursive generator. The first parameter contains left part of the string generated so far, and the second parameter is the remaining right part of the original string.
function combinations(s1, s2)
if s2:len() > 0 then
local c = s2:sub(1, 1)
local l = c:lower()
local u = c:upper()
if l == u then
combinations(s1 .. c, s2:sub(2))
else
combinations(s1 .. l, s2:sub(2))
combinations(s1 .. u, s2:sub(2))
end
else
print(s1)
end
end
So the function is called in this way.
combinations("", "ABC_-123")
You only have to store intermediate results instead of printing them.
If you are interested only in the exists function then you don't need all combinations.
local stored_string = "ABC_-123"
function exists(tested_string)
return stored_string:lower() == tested_string:lower()
end
You simply compare the stored string and the tested string in case-insensitive way.
It can be easily tested:
assert(exists("abC_-123"))
assert(not exists("abd_-123"))
How to do this?
There's native function in Lua to generate all permutations of a string, but here are a few things that may prove useful.
Substrings
Probably the simplest solution, but also the least flexible. Rather than combinations, you can check if a substring exists within a given string.
if str:find(substr) then
--code
end
If this solves your problem, I highly reccomend it.
Get all permutations
A more expensive, but still a working solution. This accomplishes nearly exactly what you asked.
function GetScrambles(str, tab2)
local tab = {}
for i = 1,#str do
table.insert(tab, str:sub(i, i))
end
local tab2 = tab2 or {}
local scrambles = {}
for i = 0, Count(tab)-1 do
local permutation = ""
local a = Count(tab)
for j = 1, #tab do
tab2[j] = tab[j]
end
for j = #tab, 1, -1 do
a = a / j
b = math.floor((i/a)%j) + 1
permutation = permutation .. tab2[b]
tab2[b] = tab2[j]
end
table.insert(scrambles, permutation)
end
return scrambles
end
What you asked
Basically this would be exactly what you originally asked for. It's the same as the above code, except with every substring of the string.
function GetAllSubstrings(str)
local substrings = {}
for i = 1,#str do
for ii = i,#str do
substrings[#substrings+1]=str:sub(ii)
end
end
return substrings
end
Capitals
You'd basically have to, with every permutation, make every possible combination of capitals with it.
This shouldn't be too difficult, I'm sure you can code it :)
Are you joking?
After this you should probably be wondering. Is all of this really necessary? It seems like a bit much!
The answer to this lies in what you are doing. Do you really need all the combinations of the given characters? I don't think so. You say you need it for case insensitivity in the comments... But did you know you could simply convert it into lower/upper case? It's very simple
local str = "hELlO"
print(str:lower())
print(str:upper())
This is HOW you should store names, otherwise you should leave it case sensitive.
You decide
Now YOU pick what you're going to do. Whichever direction you pick, I wish you the best of luck!
I am creating functions (of x) from a string in Lua. The code I am using is
function fcreate(fs)
return assert(loadstring("return function (x) return " .. fs.." end"))()
end
This works for globals, e.g.
u=fcreate("math.sin(x)")
does the right thing.
However, it does not seem to like local variables. So
local c=1
u=fcreate("math.sin(x)+c")
will not work because c is local.
Is this fixable?
"loadstring does not compile with lexical scoping", so no, it can't see locals outside the loadstring call.
Is this fixable?
That depends. Why are you using loadstring in the first place? Lua supports closures as first class values, so I can't see from your example why you'd need loadstring.
Your example:
u = fcreate("math.sin(x)+c")
Can be rewritten without the need for loadstring or your fcreate function:
u = function(x) return math.sin(x)+c end
Which of course is the same as:
function u(x) return math.sin(x) + c end
I can see a case for loadstring if you have user-configurable expressions that you wanted to compile into some other function, but your case with the local c suggests that's not the case. Are you trying to make some kinda of home-rolled lamda syntax?
Can't be done in any reasonable way. For an example of why, look at this:
function makefunction(name)
local a = 1
local b = 2
local c = 3
-- ...
return assert(loadstring("return " .. name))
end
local a = 4
local func = makefunction("a")
print(func())
If this worked, what is printed? 1 or 4? Does it capture the variable from the place where the function was loaded, even though that function doesn't exist anymore? Or does it look it up from the place where it was called?
The first would mean that the function is lexically scoped wherever it's created. Being able to access the variable after the function has exited means that the variable would need to be promoted into an upvalue dynamically, which is not something that Lua can do at the moment. As it is now, Lua can see every access to a local variable during compilation, so it knows which variables to turn into upvalues (at a performance hit) and which to keep as locals.
The second would mean that variable accesses inside a loadstring'd function would work completely different than every other access in Lua: Lua uses lexical scoping, not dynamic scoping. It'd be a huge implementation change in Lua, and an extremely inconsistent one.
So, neither is supported. You can control the environment of a dynamically loaded function, using setfenv in Lua 5.1 or the env parameter of load(...) in Lua 5.2, but neither of those let you access local variables automatically.
Something you could do if you don't need to mutate the local variables is to pass those values as arguments to the generated function. You would still need to manually specify the variables to close over but its better then nothing.
For example, you can build up your closure to look like
return (function(a,b,c)
return function(x) return print(a, x) end
end)(...)
We might do that by changing your function to look like
function fcreate(variables, fs)
local varnames = {}
local varvalues = {}
local nvars = 0
for n,v in pairs(variables) do
nvars = nvars + 1
table.insert(varnames, n)
table.insert(varvalues, v)
end
local chunk_str = (
'return (function(' .. table.concat(varnames, ',') .. ') ' ..
'return function(x) return ' .. fs .. ' end ' ..
'end)(...)'
)
return assert( loadstring(chunk_str) )( unpack(varvalues, 1, nvars) )
end
local a = 1;
local f = fcreate({a=a}, 'x+a')
print(f(1), f(2))
Sorry if this is too obvious, but I am a total newcomer to lua, and I can't find it in the reference.
Is there a NAME_OF_FUNCTION function in Lua, that given a function gives me its name so that I can index a table with it? Reason I want this is that I want to do something like this:
local M = {}
local function export(...)
for x in ...
M[NAME_OF_FUNCTION(x)] = x
end
end
local function fun1(...)
...
end
local function fun2(...)
...
end
.
.
.
export(fun1, fun2, ...)
return M
There simply is no such function. I guess there is no such function, as functions are first class citizens. So a function is just a value like any other, referenced to by variable. Hence the NAME_OF_FUNCTION function wouldn't be very useful, as the same function can have many variable pointing to it, or none.
You could emulate one for global functions, or functions in a table by looping through the table (arbitrary or _G), checking if the value equals x. If so you have found the function name.
a=function() print"fun a" end
b=function() print"fun b" end
t={
a=a,
c=b
}
function NameOfFunctionIn(fun,t) --returns the name of a function pointed to by fun in table t
for k,v in pairs(t) do
if v==fun then return k end
end
end
print(NameOfFunctionIn(a,t)) -- prints a, in t
print(NameOfFunctionIn(b,t)) -- prints c
print(NameOfFunctionIn(b,_G)) -- prints b, because b in the global table is b. Kind of a NOOP here really.
Another approach would be to wrap functions in a table, and have a metatable set up that calls the function, like this:
fun1={
fun=function(self,...)
print("Hello from "..self.name)
print("Arguments received:")
for k,v in pairs{...} do print(k,v) end
end,
name="fun1"
}
fun_mt={
__call=function(t,...)
t.fun(t,...)
end,
__tostring=function(t)
return t.name
end
}
setmetatable(fun1,fun_mt)
fun1('foo')
print(fun1) -- or print(tostring(fun1))
This will be a bit slower than using bare functions because of the metatable lookup. And it will not prevent anyone from changing the name of the function in the state, changing the name of the function in the table containing it, changing the function, etc etc, so it's not tamper proof. You could also strip the tables of just by indexing like fun1.fun which might be good if you export it as a module, but you loose the naming and other tricks you could put into the metatable.
Technically this is possible, here's an implementation of the export() function:
function export(...)
local env = getfenv(2);
local funcs = {...};
for i=1, select("#", ...) do
local func = funcs[i];
for local_index = 1, math.huge do
local local_name, local_value = debug.getlocal(2, local_index);
if not local_name then
break;
end
if local_value == func then
env[local_name] = local_value;
break;
end
end
end
return env;
end
It uses the debug API, would require some changes for Lua 5.2, and finally I don't necessarily endorse it as a good way to write modules, I'm just answering the question quite literally.
Try this:
http://pgl.yoyo.org/luai/i/tostring
tostring( x ) should hopefully be what you are looking for
If I am not wrong (and I probably will, because I actually never programmed in Lua, just read a bunch of papers and articles), internally there is already a table with function names (like locals and globals in Python), so you should be able to perform a reverse-lookup to see what key matches a function reference.
Anyway, just speculating.
But the fact is that looking at your code, you already know the name of the functions, so you are free to construct the table. If you want to be less error prone, it would be easier to use the name of the function to get the function reference (with eval or something like that) than the other way around.