References: 1. “Programming in LUA, 2 nd ed.”, Roberto Lerusalmschy Chapters “Lua Reference Manual” (included in Lua installation or online)

What is Lua?  A very lightweight scripting language Very bare-bones Easy C integration (note: NOT C++) Reasonably Fast (for a scripting language)  Used as a scripting language in many games WoW The Witcher Legend of Grimlock …  Getting it:  Documentation:  Trivia: “Lua” means moon in Portugese

Our Intro’s steps ( one lecture / mini-lab each / quiz for each ) 1. Get familiar with the non-OOP features (this lecture) 2. OOP-esque programming in Lua 3. Writing a C extension to Lua 4. Embedding Lua in a C program. 5. Integrate Lua into our Engine Note: We’re NOT going to cover a significant amount of Lua. We’ll just look at enough to get started – then it’s up to you!

Running Lua programs  For now… Create a.lua (text) file in Notepad++ Run through the command line  Eventually… No command-prompt. We’ll make ssuge contain an embedded Lua interpreter which works with our C/C++ code.

Simple example ( sample01.lua ) print(“Hello, World”) -- it has to be this…:-) save it to sample01.lua (mine is in c:\Shawnee\2014sp\etgg3802\lua) run “cmd” from the start menu

Something a little more exciting (sample02.lua) -- defines a new factorial function function fact(n) if n == 0 then return 1 else return n * fact(n - 1) end print("Enter a number: ") a = io.read("*number") -- could also be [no args] waits for enter -- "*all" reads file contents(not useful here) -- "*line" reads a line of text -- n reads n (int) characters print(a.. "! = ".. fact(a)) -- concatenation with auto-conversion

Lua types  These are the only built-in constructs in Lua nil (a non-value; useful to indicate garbage) booleans numbers (doubles, (sort of) int’s) strings (ascii 8-bit) tables (the biggie) functions userdata (we’ll see these when embedding) threads (we won’t cover these)  Note: no classes, but we can use tables to do OOP.

string examples (sample03.lua) x = "This is a \"test\"" print(x) y = string.gsub(x, "test", "quiz") print(y) -- “This is a “quiz”” z = [[This is a really long string covering four lines]] print(z) -- useful for a block "comment" q = [==[Another multi-line text]==] -- This is necessary because sometimes we'll use [[ and ]] -- for other things. e.g. a = b[c[i]] (list-like access) -- You can have any number of '=' characters. print(q) r = string.rep(“abc”, 3) print(r) -- abcabcabc

string examples, cont. print("10" + 1) -- "11" print("10 + 1") -- "10 + 1" print("15" * "3") -- "45" (auto-conversion to number) print("-5.3e-10" * "2") e-9 (auto-conversion to number) --print("hello" + 1) -- ERROR print( ) -- "1020" (auto-conversion to string) print(tostring(10).. tostring(20)) -- "1020" (preferred way)

string examples, cont. print("Enter something: ") response = io.read() n = tonumber(response) -- nil if unconvertable if n == nil then error("'".. response.. "' can't be converted to a number" ) else print(n * 2) end xlen = #x -- length of (string) x print("'".. x.. "' is ".. xlen.. " characters long") -- a wrapper for C’s printf function print(string.format("[%s, %d::%0.2f]", "hello", 5, ))

string examples, cont. s = "==qasdlkfjh==slkjh==u==" -- Extracting a sub-string subs = string.sub(s, 2, 10) -- includes start / end indicies -- finds the character *after* each ==, if there is one indx = 1 while true do new_indx, end_indx = string.find(s, "==", indx) if new_indx == nil then break elseif end_indx < #s then print("(".. new_indx.. ") = ".. string.sub(s, end_indx + 1, end_indx + 1)) end indx = new_indx + 1 end

Tables  Nearly everything in Lua is a table.  A table is an associative array A collection of key-value pairs ○ Both can be any Lua “thing” (including other tables!) Unordered Like a python dictionary or STL (C++) maps

Table example (sample04.lua) a = {} -- an empty table a.x = 15 a.y = "hello" a.z = 3.7 print(a) -- table: 003FC9B0 for k, v in pairs(a) do print("key=".. k.. ", value=".. v) end

Table example, cont. a.x = a.x + 1 a["x"] = a["x"] same as line before print(a.x) print(a.q) -- nil: a non-existent key (not an error...) b = a -- Note: a and b are *pointers* to the *same* table b.y = "goodbye" print(a.y) -- goodbye

Table example, cont. -- sorting the keys of a table temp_keys = {} for k, v in pairs(a) do temp_keys[#temp_keys + 1] = k end table.sort(temp_keys) for _, v in pairs(temp_keys) do -- _ is a "don't-care" variable print("a[".. v.. "] = ".. a[v]) end

Table example, cont. -- creating a table with (integer) values c = {[5] = "abc", [6] = "def"} -- integer keys c[7] = "xyz" -- new int key for i = 5, 7 do print(c[i]) end -- Looks a lot like an array, doesn't it in fact there is NO array type in lua. This is it!

Table example, cont. -- lua "lists" start with index 1 by convention. d = {} for i = 1, 10 do d[i] = i * i + 2 end print(#d) (length -- only works for 1-based "lists") print(d[#d]) (last element) print(d[10]) print(d["10"]) -- nil print(d["+10"]) -- nil (not the same key as "10")

Table example, cont. -- table with table values (a 2d table) times_table = {} for i = 1, 10 do times_table[i] = {} for j = 1, 10 do times_table[i][j] = i * j end -- pull out result for 5 * 7 print(times_table[5][7]) -- or times_table[7][5] here

[File] I/O (sample5.lua)  (This is the more general method) And a taste of OOP in Lua -- Wrapping in the assert call will fail if io.open returns nil (error) local f = assert(io.open("test.txt", "r")) count = 1 while true do -- Note the colon here. f is an "object" and we're calling -- the read "method" L = f:read("*line")-- reads one line of text. Could also be -- "*all": reads entire file -- n: Reads n characters if L == nil then break end print("Line #".. count.. " = '".. L.. "'") count = count + 1 end f:close()

local vs. global variables  Normally all variables are global. Regardless of where they're defined  Put the local keyword before the name when creating to limit it to that block  It's good practice to use locals to hide "unncessary" variables Encapsulation

local example (sample06.lua) x = a global function foo() y = also a global print(x) local x = 11 print(x) (masks the global x) if x < 50 then local x = 12 print(x) masks the local above end print(x) (the 12 is no longer masking) end foo() print(x)-- 10 (function locals are gone)

command-line args  An alternate way to call lua from command line: lua script_name.lua arg1 arg2 … lua sample1_07.lua abc -- command-line arguments test for i, val in pairs(arg) do print("arg#".. i.. " = '".. val.. "'") end