In lua I'm using someone elses function that takes variable number of arguments. What I would like to be able to do is build the argument list via loop. Is this possible?
Example function:
printResult = ""
function print (...)
for i,v in ipairs(arg) do
printResult = printResult .. tostring(v) .. "\t"
end
printResult = printResult .. "\n"
end
I tried
print({"test","test2"})
But that just passes one argument (the table) to the function
You are looking for the table.unpack function. You can build the arguments to the vararg function you want to call in a table. Calling table.unpack on the table will expand the table into an argument list. Like so,
args = {}
for i = 1, 4 do
args[#args+1] = i * i * math.pi
end
print(table.unpack(args))
Also, you will need in the print function you posted to gather all those arguments into the arg list that you are using...
function print (...)
printResult = ""
arg = {...}
for i,v in ipairs(arg) do
printResult = printResult .. tostring(v) .. "\t"
end
printResult = printResult .. "\n"
return printResult
end
Finally, there is already a way to accomplish what you are trying to do using table.concat.
function print(...)
return table.concat({...}, "\t").."\n"
end
Related
I am trying to write a curry function in lua 5.2. My code looks like this:
function add(a, b)
return a + b
end
function curry(func, value)
return (function (...)
return func(value, table.unpack(arg))
end)
end
add2 = curry(add, 2)
print(add2(3))
The parameter arg however does not contain the value passed into the add2 function.
When I try and run the example from the Lua documentation it errors because arg is nil.
printResult = ""
function print (...)
for i,v in ipairs(arg) do -- arg is nil
printResult = printResult .. tostring(v) .. "\t"
end
printResult = printResult .. "\n"
end
How can I use variable length functions in 5.2 if this is not working?
Edit:
As user #siffiejoe has pointed out, my function here is just doing partial application, not proper currying. Here is my implementation of a proper curry function in lua using the error fix from the accepted answer.
function curry(func, params)
return (function (...)
local args = params or {}
if #args + #{...} == debug.getinfo(func).nparams then
local args = {table.unpack(args)}
for _,v in ipairs({...}) do
table.insert(args, v)
end
return func(table.unpack(args))
else
local args = {table.unpack(args)}
for _,v in ipairs({...}) do
table.insert(args, v)
end
return curry(func, args)
end
end)
end
Feel free to suggest changes and add test cases here
Since Lua 5.1, arg in this context has been replaced by ... (except that the latter is a list instead of a table).
So, table.unpack(arg) should be just ....
See Breaking Changes. The Lua Reference manuals are very good and this section in particular is highly useful.
Assuming I have a piece of code such as the following
aTable = {aValue=1}
aTable_mt = {}
print(aTable)
What must I do to make Lua print something like aTable current aValue = 1 as opposed to table: 0x01ab1d2.
So far I've tried setting the __tostring metamethod but that doesn't seem to be invoked by print. Is there some metamethod I've been missing or does the answer have nothing to do with metamethods?
__tostring works:
aTable = {aValue=1}
local mt = {__tostring = function(t)
local result = ''
for k, v in pairs(t) do
result = result .. tostring(k) .. ' ' .. tostring(v) .. ''
end
return result
end}
setmetatable(aTable, mt)
print(aTable)
This prints aValue 1 (with one extra whitespace, remove it in real code). The aTable part is not available, because aTable is a variable that references the table, not the content of the table itself.
I'm not sure how you set the metamethod, but the following code prints "stringified" for me:
local aTable = {a = 1, b = 2}
setmetatable(aTable, {__tostring = function() return "stringified" end})
print(aTable)
If you want lua to generally print all tables human readable, you could
hook up/overwrite the print function:
local orig_print = print
print = function(...)
local args = {...}
for i,arg in ipairs(args) do
if type(arg) == 'table' then
args[i] = serialize(arg)
end
end
orig_print(table.unpack(args))
end
serialize could be serpent or some other lib from here
Note that this must be done before any other module/script is loaded.
Okay I am working on a script for my Oxide Lua Plugin, and I am also just learning Lua Script so I am not real sure how to do this.
-- *******************************************
-- Broadcasts a Server Notification
-- *******************************************
function PLUGIN:cmdNotice( netuser, args )
table.concat(args," ")
local allnetusers = rust.GetAllNetUsers()
if (allnetusers) then
for i=1, #allnetusers do
local netuser = allnetusers[i]
rust.Notice(netuser, args[1]))
rust.SendChatToUser(netuser, "Message Sent:" .. args[1])
end
end
end
What I am trying to do is fix this so I do not have to manually encase my notice in "".
For example, as the code stands, while I am in game in rust if I use the /notice command I have two outcomes.
Example 1
/notice hello everone
will only produce
hello
but if I do
/notice "hello everyone"
will give the entire message. So I am a little confused.
So my new code should look like this
-- *******************************************
-- Broadcasts a Server Notification
-- *******************************************
function PLUGIN:cmdNotice( netuser, args )
table.concat(args," ")
local allnetusers = rust.GetAllNetUsers()
if (allnetusers) then
for i=1, #allnetusers do
local netuser = allnetusers[i]
rust.Notice(netuser, table.concat(args, " " ))
rust.SendChatToUser(netuser, "Message Sent:" .. table.concat(args, " "))
end
end
end
Edit 3/15/2014
Okay cool so in a since I can also do this as well correct?
function PLUGIN:cmdNotice( netuser, args )
if (not args[1]) then
rust.Notice( netuser, "Syntax: /notice Message" )
return
end
local allnetusers = rust.GetAllNetUsers()
if allnetusers then
for i=1, #allnetusers do
local netuser = allnetusers[i]
local notice_msg = table.concat(args," ")
rust.Notice(netuser, notice_msg)
rust.SendChatToUser(netuser, "Message Sent:" .. notice_msg)
end
end
end
To clarify what #EgorSkriptunoff said, table.concat returns the joined table, but it does not change the value of args. Since you don't save the joined return value, your line 1 inside the function is useless. As an alternative to his approach, you could do rust.SendChatToUser ( netuser, "Message Sent:" .. table.concat(args, " " ).
My guess is that you were thinking (?) that the joined strings would be saved in the args table as the first item in the table? That's not what happens. The table itself remains unchanged, so when you print args[1], you get only the first string of the array. It "works" when you quote the message because in that case the entire message goes in as one thing, and the array only has an arg[1].
Here's what is going on
t = { "hello", "I", "must", "be", "going"}
-- Useless use of concat since I don't save the return value or use it
table.concat(t, " ")
print(t) -- Still an unjoined table
print(t[1]) -- Prints only "hello"
print(table.concat(t, " ")) -- Now prints the return value
Edit: In response to the follow-up question, see my comments in the code below:
function PLUGIN:cmdNotice( netuser, args )
table.concat(args," ") -- This line is not needed.
local allnetusers = rust.GetAllNetUsers()
-- Lua doesn't count 0 as false, so the line below probably doesn't do
-- what you think it does. If you want to test whether a table has more
-- than 0 items in it, use this:
-- if #allnetusers > 0 then...
if allnetusers then
for i=1, #allnetusers do
local netuser = allnetusers[i]
rust.Notice(netuser, table.concat(args, " " ))
rust.SendChatToUser(netuser, "Message Sent:" .. table.concat(args, " "))
end
end
end
I was testing the scope for Lua and noticed something unexpected. The following code does not print the localMainVariable.
function functionScope()
print( "\nIn function")
print( "globalMainVariable: " .. globalMainVariable )
if (localMainVariable ~= nil) then print( "localMainVariable: " .. localMainVariable ) end
end
globalMainVariable = "Visible"
local localMainVariable = "Visible"
functionScope()
But the following code does print localMainVariable.
globalMainVariable = "Visible"
local localMainVariable = "Visible"
function functionScope()
print( "\nIn function")
print( "globalMainVariable: " .. globalMainVariable )
if (localMainVariable ~= nil) then print( "localMainVariable: " .. localMainVariable ) end
end
functionScope()
I know it has something to do with where the localMainVariable was declared, but I thought making it local would limit the scope of the variable. What is the actual rule?
Thanks
The scope of a local variable begins at the first statement after its
declaration and lasts until the last non-void statement of the
innermost block that includes the declaration.
Lua manual
I am trying to build an elegant transpose function using functions mapn and zip in Lua.
The mapn and zip are as follows (From the lua book):
function map(func, array)
local new_array = {}
for i,v in ipairs(array) do
new_array[i] = func(v)
end
return new_array
end
function mapn(func, ...)
local new_array = {}
local i=1
local arg_length = table.getn(arg)
while true do
local arg_list = map(function(arr) return arr[i] end, arg)
if table.getn(arg_list) < arg_length then return new_array end
new_array[i] = func(unpack(arg_list))
i = i+1
end
end
These work as expected.
I then define zip and transpose as:
function zip(...)
return mapn(function(...) return {...} end,...)
end
function transpose(...)
return zip(unpack(...))
end
Now transpose({{1,2},{3,4},{5,6}}) produces {{1,3,5},{2,4,6}} as expected.
But transpose({{1,2},{3,4},{5}}) does not produce {{1,3,5},{2,4}}. It only produces one row.
How can I get it to produce the result I wish for?
I just decided to write an "inelegant" function instead. It seems there's no smooth way to use mapn and friends.
function transp(L)
local n=#L
local m,M=1e42,0
--Get the beginning and end of resultant transpose list.
for i=1,n do
for k,v in pairs(L[i]) do
if M<k then M=k end
if m>k then m=k end
end
end
local nt={}
for i=m,M do
local rt={}
for j=1,n do
rt[j]=L[j][i]
end
table.insert(nt,rt)
end
return nt
end
Please critique and improve this candidate solution.
I fixed a few things in your code and I think it works now as intended, I've added comments inline.
function map(func, array)
local new_array = {}
for i, v in ipairs(array) do
new_array[#new_array + 1] = func(v)
end
return new_array
end
function mapn(func, ...)
-- Variadic arguments bound to an array.
local arrays = {...}
local new_array = {}
-- Simple for-loop.
local i = 1
while true do
local arg_list = map(function(arr) return arr[i] end, arrays)
if #arg_list == 0 then
break
end
new_array[i] = func(unpack(arg_list))
i = i + 1
end
return new_array
end
-- Using 'mapn' instead of 'map' (probably how you intended).
function zip(...)
return mapn(function(...) return {...} end,...)
end
-- Same as before.
function transpose(...)
return zip(unpack(...))
end
Usage example:
for _, row in pairs(transpose({{1,2},{3,4},{5}})) do
for _, col in pairs(row) do io.write(col .. ' ') end
io.write('\n')
end
-- Output: 1 3 5
-- 2 4
The {5} in your example is being ignored because of this line:
if table.getn(arg_list) < arg_length then return new_array end
What you may want to do instead is break out of the loop only when arg_list is empty.
This will then give the result you want provided that the rows are monotonically increasing in length.
For the more general case, when later rows may be shorter than earlier ones
(e.g. {{1,2},{3,4,5},{6}}), you will need to keep track of the row lengths to allow for holes. This can be done by adding an optional argument (and extra return value) to map to indicate the maximum index i for which func(array[i]) was evaluated:
function map(func, array, len)
local new_array = {}
len = len or #array
for i=1,len do
new_array[i] = func(array[i])
end
return new_array, len
end
function mapn(func, ...)
local new_array = {}
local i=1
local arg_length = select('#', ...)
local args = {...}
while true do
local arg_list, num_results = map(function(arr) return arr[i] end, args, arg_length)
if not next(arg_list) then return new_array end
new_array[i] = func(unpack(arg_list, 1, num_results))
i = i+1
end
end
function zip(...)
return mapn(function(...) return {...} end,...)
end
function transpose(...)
return zip(unpack(...))
end