10 replies to this topic

[Yurij]

Title: Getting nil trying to use the peripheral api

write("Choose side: ")
side = read()
if peripheral.isPresent(side) then
end

While trying this code I am getting some wonky behaviour.
Most of the time I get the "attempt to call nil" error on the isPresent call, but sometimes it works

Writing it in the lua promt works fine

[Symmetryc]

I don't think this is the case, but do you have "side" defined as a global variable somewhere else?

[Engineer]

Symmetryc, on 13 June 2013 - 12:39 PM, said:

I don't think this is the case, but do you have "side" defined as a global variable somewhere else?

That should not matter, because he is redefining it.

Try this right here:

local side = nil
local sides = rs.getSides()
repeat
    write("Choose side: ")
    side = read():lower() -- To make sure its all lowered case, wich matters
until sides[side] -- See what I did here? This is a reference to TheOriginalBIT :P/>
if peripheral.isPresent( side ) then
end

This code keeps asking until you have entered a valid side.

[Symmetryc]

Engineer, on 13 June 2013 - 01:16 PM, said:

Symmetryc, on 13 June 2013 - 12:39 PM, said:

I don't think this is the case, but do you have "side" defined as a global variable somewhere else?

That should not matter, because he is redefining it.

Yeah, I didn't think that it was the case :/.

IIRC, peripheral.isPresent() doesn't error with attempt to call nil, even if the side isn't valid, though.

[Yurij]

Engineer, on 13 June 2013 - 01:16 PM, said:

Symmetryc, on 13 June 2013 - 12:39 PM, said:

I don't think this is the case, but do you have "side" defined as a global variable somewhere else?

That should not matter, because he is redefining it.

Try this right here:

local side = nil
local sides = rs.getSides()
repeat
	write("Choose side: ")
	side = read():lower() -- To make sure its all lowered case, wich matters
until sides[side] -- See what I did here? This is a reference to TheOriginalBIT :P/>/>
if peripheral.isPresent( side ) then
end

This code keeps asking until you have entered a valid side.

That code isn't working for me. It just loops.

[Engineer]

What are you putting in? The sides are:

left
right
top
bottom
front
back

Edit: oops, just realised.. Try this instead:

local sides = {}
for k, v in pairs(rs.getSides()) do
  sides[v] = true
end
local side = nil
repeat
   side = read():lower()
until sides[side]
if peripheral.isPresent( side ) then
   print('hooray!')
end

[theoriginalbit]

Engineer, on 13 June 2013 - 06:11 PM, said:

Edit: oops, just realised.. Try this instead:

local sides = {}
for k, v in pairs(rs.getSides()) do
  sides[v] = true
end
local side = nil
repeat
   side = read():lower()
until sides[side]
if peripheral.isPresent( side ) then
   print('hooray!')
end

Much better, I was just about to point that out
BTW you have to admit that a lookup is much better than a looping.

[Bomb Bloke]

Is that really the case? Doesn't Lua have to perform a loop in order to perform the lookup anyway?

Though I sorta suspect it does that regardless. Single loop versus a double loop? Dunno.

[theoriginalbit]

Bomb Bloke, on 14 June 2013 - 03:30 AM, said:

Is that really the case? Doesn't Lua have to perform a loop in order to perform the lookup anyway?
Though I sorta suspect it does that regardless. Single loop versus a double loop? Dunno.

Tables, in LuaJ, are HashMaps, so no Lua does not have to perform a loop to perform a lookup.

[Bomb Bloke]

Ah, understanding hashmaps explains an awful lot about a lot of things... thanks!

[Yurij]

Engineer, on 13 June 2013 - 06:11 PM, said:

What are you putting in? The sides are:

left
right
top
bottom
front
back

Edit: oops, just realised.. Try this instead:

local sides = {}
for k, v in pairs(rs.getSides()) do
  sides[v] = true
end
local side = nil
repeat
   side = read():lower()
until sides[side]
if peripheral.isPresent( side ) then
   print('hooray!')
end

Thanks.
Looks like it's working now