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| − | == Debugging ==
| + | #REDIRECT [[Welcome to NETIO resources & projects & documentation overview]] |
| − | To debug your code, use [[Function log()|log()]] and [[Function logf()|logf()]] functions. See the output in system events log.
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| − | | |
| − | == Data types and variables ==
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| − | Lua supports these data types:
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| − | * <i>nil</i> (to assign <i>nil</i> value effectively deletes the variable)
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| − | * <i>boolean</i> (falsy values are <i>nil</i> and <i>false</i> only; "" and 0 evaluates as <i>true</i>)
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| − | * <i>number</i> (decimals only in standard Lua, integers only in Netio Lua)
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| − | * <i>string</i> (same strings share same address, so equality operator measures both address and value)
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| − | * <i>tables</i> are associative arrays. (Tables with numeric indices are, well, just arrays.)
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| − | | |
| − | local numbers = {2,3,7,5} -- array (first index = 1)
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| − | local dictionary = {one=1, two=2, three=3} -- table
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| − | local numbersZeroBased = {[0]=2,3,7,5} -- array (first index = 0)
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| − | | |
| − | <i>local</i> keyword limits the variable scope to the block (ended by <i>end</i>) where it is declared. To access an <i>upvalue</i> (variable defined outside of the scope), just omit the <i>local</i> keyword.
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| − | | |
| − | == Operators ==
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| − | Lua has its own manners:
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| − | * <code>~=</code> is inequality operator
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| − | * <code>..</code> is string concatenation (don't use plus)
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| − | * <code><s>i++</s></code> no increment/decrement operator <code>i = i + 1</code>
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| − | * <code><s>max = a<b ? b : a</s></code> no ternary operator. Use (and get used to) <i>and idiom</i> instead: <code>max = (a<b) and b or a</code>
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| − | * <i>or idiom</i> works: <code>x = x or 42</code> is equivalent to <code>if not x then x = 42 end</code>
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| − | | |
| − | == Conditions ==
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| − | Lua conditions has casual syntax, see [https://www.lua.org/pil/4.3.1.html here]. Just keep in mind to merge <code>else</code> and <code>if</code> to <code>elseif</code> or multiple <code>end</code>s are required.
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| − | | |
| − | Note that falsy values are <i>nil</i> and <i>false</i> only. Empty string and 0 evaluates as true. If you come from C, you might be surprised by following snippet:
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| − | | |
| − | if devices.system.output1_consumption then
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| − | -- always happens, even if the consumption is 0
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| − | log("Outlet 1 supplies power")
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| − | end
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| − | | |
| − | if not devices.system.output1_consumption then
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| − | -- never happens, even if the consumption is 0
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| − | log("Outlet 1 is idle")
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| − | end
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| − | | |
| − | == Loops ==
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| − | Lua has <code>break</code> statement, but no <code>continue</code> (use condition inside loop instead). Additionally, Netio Lua implementation limits the loop iterations to 32k.
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| − | | |
| − | === While ===
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| − | While syntax is not different to other languages:
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| − | local i = 0
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| − | while i~=3 do
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| − | i = i + 1
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| − | logf("%d",i)
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| − | end
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| − | | |
| − | === Repeat until ===
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| − | Repeat until syntax is the same as Pascal's, other languages have similar do-while loops:
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| − | local i = 0
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| − | repeat
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| − | i = i + 1
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| − | logf("%d",i)
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| − | until i==3
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| − | | |
| − | === Numeric for ===
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| − | Arrays in Lua are one-based (in indices are not specified, the first one is 1, not 0).
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| − | local arr = {2,3,7,5}
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| − | for i=1,#arr do logf("%d",arr[i]) end
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| − | <code><b>for</b> initVar,limit,increment <b>do</b></code>
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| − | * <i>number assignment</i> <code>initVar</code> inits loop-local variable
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| − | * <i>number</i> <code>limit</code> loops until initVar reaches this value
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| − | * <i>optional number</i> <code>increment</code> after each loop initVar increment by this value (default 1)
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| − | | |
| − | === Generic for ===
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| − | Is rather sophisticated. Most common example (the order of elements in <code>pairs()</code> is not guaranteed):
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| − | local tab = {one=1, two=2, three=3}
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| − | for key,val in pairs(tab) do logf("%s:%d",key,val) end
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| − | Generic for syntax
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| − | <b>for</b> var_1, ..., var_n <b>in</b> explist <b>do</b> block end
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| − | is equivalent to (Full explanation [https://www.lua.org/pil/7.2.html here].)
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| − | do
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| − | local _f, _s, _var = explist
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| − | while true do
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| − | local var_1, ... , var_n = _f(_s, _var)
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| − | _var = var_1
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| − | if _var == nil then break end
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| − | block
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| − | end
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| − | end
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| − | | |
| − | Iterator closure that holds its state
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| − | function iter(a)
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| − | local i = 0
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| − | return function()
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| − | i = i+1
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| − | return a[i]
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| − | end
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| − | end
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| − |
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| − | local arr = {2,3,7,5}
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| − | for value in iter(arr) do
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| − | logf("%d",value)
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| − | end
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| − | | |
| − | Stateless iterator (in this case returns variable list: key and value)
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| − | function iter(a,i)
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| − | i = i+1
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| − | if a[i] then return i,a[i] end
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| − | end
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| − |
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| − | local arr = {2,3,7,5}
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| − | for k,v in iter,arr,0 do
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| − | logf("%d:%d",k,v)
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| − | end
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| − | | |
| − | Same effect using <code>ipairs()</code> Lua function (without initial state)
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| − | for k,v in ipairs(arr) do
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| − | logf("%d:%d",k,v)
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| − | end
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| − | | |
| − | Now return to the most common example above using <code>pairs()</code> Lua function and read about <code>pairs()</code> and <code>ipairs()</code> implementation [https://www.lua.org/pil/7.3.html here].
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| − | | |
| − | == Functions ==
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| − | | |
| − | Lua allows multiple results (comma separated):
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| − | | |
| − | function diskSpace()
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| − | return devices.system.freeSpace, devices.system.totalSpace
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| − | end
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| − |
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| − | logf("Free space: %d MB", diskSpace()) -- only first return value is used
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| − | local free,total = diskSpace() -- values are stored into LHS var-list
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| − | logf("Free space: %d %%", 100*free/total)
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| − | | |
| − | Variable-length arguments are also available:
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| − | | |
| − | function sum(...)
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| − | local result = 0
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| − | for _,v in ipairs(arg) do
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| − | result = result + v
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| − | end
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| − | return result
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| − | end
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| − |
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| − | logf("Sum: %d", sum(2,3,5))
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