Lua for TerraME: A Short Introduction Pedro Ribeiro de Andrade São José dos Campos, 2011

Lua  Robust: it has been used in many industrial applications.  Fast: several benchmarks show Lua as the fastest language in the realm of interpreted scripting languages.  Portable: Lua is distributed in a small package and builds out-of- the-box in all platforms that have an ANSI/ISO C compiler.  Embeddable: it can be embeded easily into other applications.  Powerful (but simple): Lua provides meta-mechanisms for implementing features, instead of having a host of features directly in the language.  Small: The tarball for Lua takes 860K uncompressed. The source contains around lines of C. Under Linux, the interpreter takes 153K and the library, 203K.  Free: distributed under MIT license

Lua and the Web Where is Lua?  Inside Brazil  Petrobras, the Brazilian Oil Company  Embratel (the main telecommunication company in Brazil)  many other companies  Outside Brazil  Lua is used in hundreds of projects, both commercial and academic  CGILua still in restricted use  until recently all documentation was in Portuguese LUA is the language of choice for computer games [Ierusalimschy et al, 1996] source: the LUA team

Variables and Values  Case sensitive  semicolon may optionally follow any statement a = 1 b = a*2 a = 1; b = a*2 a = 1 b = a*2 print(a) print(b)

Types  nil  boolean  number  string  table  function

nil  Everything that does not exist print(type(c)) c = 10 print(type(c)) print(type(c > 2)) c = nil print(type(c)) print(type("a string!!")) print(type(print))

Boolean  false/true  nil and false are false, everything else is true  zero and the empty string are true in conditional tests  operators and, or, and not print(true and false) print(true and (false or true)) print(false or (true and false) or (true and true))

Number  the only type for numeric values  double-precision floating-point number  arithmetic operators: +, –, *, /  exponent (^) and modulo (%)  boolean operators (, =, ~=, and ==). A = * 4 a = A ^ 2 b = A % 7 print(a) print(b) print(a > b) print(b ~= 2)

Parentheses  Always optional (except in the case of function call)  When in doubt, use parentheses a+-i (a+(-i)) < ((b/2)+1) 5+x^2*8 5+((x^2)*8) a (a < y) and (y <= z) –x^y^z –(x^(y^z))

String  single or double quotes  operator.. print("hello") print('hello') x = 2 print ("x = "..x)

If statement  An if statement tests condition and executes its then-part or its else-part (optional) accordingly. a = 6; b = 5 if a<0 then print("a < 0") end if a = b") end if a<b then print("a < b") elseif a < b + 5 then print("b < a < b+5") else print("a > b+5") end

For statement  A numeric for has the following syntax: for var = exp1, exp2, exp3 do something end  That loop will execute something for each value of var from exp1 to exp2, using exp3 as the step to increment var. This third expression is optional; for i = 1, 10 do print(i) end for i = 1, 10, 2 do print(i) end

Table  The only structured data type.  Implements associative arrays, which can be indexed not only with numbers, but also with strings or any other value of the language, except nil. x = {1,3,2,6,4,3,7} print(x[1]) x[1] =x[2] + x[3] print(x[1]) print(table.getn(x)) for i = 1, table.getn(x) do print(x[i]) end

Table  Table values can be named loc = { cover = "forest", distRoad = 0.3, distUrban = 2 } print(loc["cover"]) print(loc.cover) loc.distRoad = loc.distRoad^2 loc.distTotal = loc.distRoad + loc.distUrban print(loc.distTotal) loc.deforestationPot = 1/loc.distTotal print(loc.deforestationPot)

Function  A function can carry out a specific task (commonly called procedure) or compute and return values.  A function is a first-class value in Lua.  Functions can be stored in variables and in tables, can be passed as arguments, and can be returned by other functions, giving great flexibility to the language. print(8*9, 9/8) a = math.sin(3) + math.cos(10)

High-order Function  Functions can also be parameters to other functions. This kind of function is what we call a higher-order function. x={1, 3, 2, 6, 4} function myprint(a) print(a) end table.foreach(x, myprint) table.foreach(x, function(a) print(a) end) table.foreach(x, print)

Tables with functions  Table may have their own functions. loc = { cover = "forest", distRoad = 0.3, distUrban = 2 } loc.deforestPot = function(myloc) return 1/(myloc.distRoad + myloc.distUrban) end print(loc.deforestPot(loc)) print(loc:deforestPot())

Tables with functions  We can declare a class in Lua by creating a function that takes a table constructor as argument. function MyLocation(locdata) locdata.covertype = "forest" locdata.deforPot = function(self) return 1/(self.distRoad + self.distUrban) end return locdata end loc = MyLocation({distRoad = 0.3, distUrban = 2}) loc = MyLocation{distRoad = 0.3, distUrban = 2} print(loc.covertype) print(loc:deforPot())

Standard libraries  Basic (print, type, tostring, tonumber, …)  String (string.find, string.gsub, string.format, …)  Table (table.insert, table.remove, table.sort, table.getn …)  Math (math.random, math.sin, math.exp, …)  IO (io.open, io.read, io.close, …)  OS (os.clock, os.execute, …)  Debug (debug.getinfo, debug.getlocal, …)

Comments  double hyphen (--) until the end of the line.  block comments start with --[[ and run until ]] print("hello") -- print("hello") --[[ print(10) -- no action (comment) --]]