Merge pull request #555 from iirelu/lua-linewidth-80

[lua/en] Normalised Lua's doc to a width of 80 characters

lua.html.markdown

@@ -12,15 +12,13 @@ filename: learnlua.lua
      Adding two ['s and ]'s makes it a
      multi-line comment.
 --]]
-
+--------------------------------------------------------------------------------
-----------------------------------------------------
 -- 1. Variables and flow control.
-----------------------------------------------------
+--------------------------------------------------------------------------------
 
 num = 42  -- All numbers are doubles.
--- Don't freak out, 64-bit doubles have 52 bits for
+-- Don't freak out, 64-bit doubles have 52 bits for storing exact int
--- storing exact int values; machine precision is
+-- values; machine precision is not a problem for ints that need < 52 bits.
--- not a problem for ints that need < 52 bits.
 
 s = 'walternate'  -- Immutable strings like Python.
 t = "double-quotes are also fine"
@@ -60,8 +58,8 @@ aBoolValue = false
 -- Only nil and false are falsy; 0 and '' are true!
 if not aBoolValue then print('twas false') end
 
--- 'or' and 'and' are short-circuited.
+-- 'or' and 'and' are short-circuited. This is similar to the a?b:c operator
--- This is similar to the a?b:c operator in C/js:
+-- in C/js:
 ans = aBoolValue and 'yes' or 'no'  --> 'no'
 
 karlSum = 0
@@ -81,10 +79,9 @@ repeat
   num = num - 1
 until num == 0
 
-
+--------------------------------------------------------------------------------
-----------------------------------------------------
 -- 2. Functions.
-----------------------------------------------------
+--------------------------------------------------------------------------------
 
 function fib(n)
   if n < 2 then return n end
@@ -93,8 +90,8 @@ end
 
 -- Closures and anonymous functions are ok:
 function adder(x)
-  -- The returned function is created when adder is
+  -- The returned function is created when adder is called, and remembers the
-  -- called, and remembers the value of x:
+  -- value of x:
   return function (y) return x + y end
 end
 a1 = adder(9)
@@ -102,10 +99,9 @@ a2 = adder(36)
 print(a1(16))  --> 25
 print(a2(64))  --> 100
 
--- Returns, func calls, and assignments all work
+-- Returns, func calls, and assignments all work with lists that may be
--- with lists that may be mismatched in length.
+-- mismatched in length. Unmatched receivers are nil; unmatched senders are
--- Unmatched receivers are nil;
+-- discarded.
--- unmatched senders are discarded.
 
 x, y, z = 1, 2, 3, 4
 -- Now x = 1, y = 2, z = 3, and 4 is thrown away.
@@ -118,16 +114,15 @@ end
 x, y = bar('zaphod')  --> prints "zaphod  nil nil"
 -- Now x = 4, y = 8, values 15..42 are discarded.
 
--- Functions are first-class, may be local/global.
+-- Functions are first-class, may be local/global. These are the same:
--- These are the same:
 function f(x) return x * x end
 f = function (x) return x * x end
 
 -- And so are these:
 local function g(x) return math.sin(x) end
 local g = function(x) return math.sin(x) end
--- Equivalent to local function g(x)..., except referring
+-- Equivalent to local function g(x)..., except referring to g in the function
--- to g in the function body won't work as expected.
+-- body won't work as expected.
 local g; g  = function (x) return math.sin(x) end
 -- the 'local g' decl makes g-self-references ok.
 
@@ -136,19 +131,16 @@ local g; g  = function (x) return math.sin(x) end
 -- Calls with one string param don't need parens:
 print 'hello'  -- Works fine.
 
--- Calls with one table param don't need parens
+-- Calls with one table param don't need parens either (more on tables below):
--- either (more on tables below):
 print {} -- Works fine too.
 
-
+--------------------------------------------------------------------------------
-----------------------------------------------------
 -- 3. Tables.
-----------------------------------------------------
+--------------------------------------------------------------------------------
 
--- Tables = Lua's only compound data structure;
+-- Tables = Lua's only compound data structure; they are associative arrays.
---          they are associative arrays.
+-- Similar to php arrays or js objects, they are hash-lookup dicts that can
--- Similar to php arrays or js objects, they are
+-- also be used as lists.
--- hash-lookup dicts that can also be used as lists.
 
 -- Using tables as dictionaries / maps:
 
@@ -164,14 +156,13 @@ t.key2 = nil   -- Removes key2 from the table.
 u = {['@!#'] = 'qbert', [{}] = 1729, [6.28] = 'tau'}
 print(u[6.28])  -- prints "tau"
 
--- Key matching is basically by value for numbers
+-- Key matching is basically by value for numbers and strings, but by identity
--- and strings, but by identity for tables.
+-- for tables.
 a = u['@!#']  -- Now a = 'qbert'.
 b = u[{}]     -- We might expect 1729, but it's nil:
--- b = nil since the lookup fails. It fails
+-- b = nil since the lookup fails. It fails because the key we used is not the
--- because the key we used is not the same object
+-- same object as the one used to store the original value. So strings &
--- as the one used to store the original value. So
+-- numbers are more portable keys.
--- strings & numbers are more portable keys.
 
 -- A one-table-param function call needs no parens:
 function h(x) print(x.key1) end
@@ -191,16 +182,15 @@ v = {'value1', 'value2', 1.21, 'gigawatts'}
 for i = 1, #v do  -- #v is the size of v for lists.
   print(v[i])  -- Indices start at 1 !! SO CRAZY!
 end
--- A 'list' is not a real type. v is just a table
+-- A 'list' is not a real type. v is just a table with consecutive integer
--- with consecutive integer keys, treated as a list.
+-- keys, treated as a list.
 
-----------------------------------------------------
+--------------------------------------------------------------------------------
 -- 3.1 Metatables and metamethods.
-----------------------------------------------------
+--------------------------------------------------------------------------------
 
--- A table can have a metatable that gives the table
+-- A table can have a metatable that gives the table operator-overloadish
--- operator-overloadish behavior. Later we'll see
+-- behavior. Later we'll see how metatables support js-prototypey behavior.
--- how metatables support js-prototypey behavior.
 
 f1 = {a = 1, b = 2}  -- Represents the fraction a/b.
 f2 = {a = 2, b = 3}
@@ -221,10 +211,9 @@ setmetatable(f2, metafraction)
 
 s = f1 + f2  -- call __add(f1, f2) on f1's metatable
 
--- f1, f2 have no key for their metatable, unlike
+-- f1, f2 have no key for their metatable, unlike prototypes in js, so you must
--- prototypes in js, so you must retrieve it as in
+-- retrieve it as in getmetatable(f1). The metatable is a normal table with
--- getmetatable(f1). The metatable is a normal table
+-- keys that Lua knows about, like __add.
--- with keys that Lua knows about, like __add.
 
 -- But the next line fails since s has no metatable:
 -- t = s + s
@@ -236,11 +225,12 @@ myFavs = {food = 'pizza'}
 setmetatable(myFavs, {__index = defaultFavs})
 eatenBy = myFavs.animal  -- works! thanks, metatable
 
--- Direct table lookups that fail will retry using
+--------------------------------------------------------------------------------
--- the metatable's __index value, and this recurses.
+-- Direct table lookups that fail will retry using the metatable's __index
+-- value, and this recurses.
 
--- An __index value can also be a function(tbl, key)
+-- An __index value can also be a function(tbl, key) for more customized
--- for more customized lookups.
+-- lookups.
 
 -- Values of __index,add, .. are called metamethods.
 -- Full list. Here a is a table with the metamethod.
@@ -261,12 +251,12 @@ eatenBy = myFavs.animal  -- works! thanks, metatable
 -- __newindex(a, b, c)             for a.b = c
 -- __call(a, ...)                  for a(...)
 
-----------------------------------------------------
+--------------------------------------------------------------------------------
 -- 3.2 Class-like tables and inheritance.
-----------------------------------------------------
+--------------------------------------------------------------------------------
 
--- Classes aren't built in; there are different ways
+-- Classes aren't built in; there are different ways to make them using
--- to make them using tables and metatables.
+-- tables and metatables.
 
 -- Explanation for this example is below it.
 
@@ -286,22 +276,20 @@ mrDog = Dog:new()                          -- 7.
 mrDog:makeSound()  -- 'I say woof'         -- 8.
 
 -- 1. Dog acts like a class; it's really a table.
--- 2. function tablename:fn(...) is the same as
+-- 2. "function tablename:fn(...)" is the same as
---    function tablename.fn(self, ...)
+--    "function tablename.fn(self, ...)", The : just adds a first arg called
---    The : just adds a first arg called self.
+--    self. Read 7 & 8 below for how self gets its value.
---    Read 7 & 8 below for how self gets its value.
 -- 3. newObj will be an instance of class Dog.
--- 4. self = the class being instantiated. Often
+-- 4. "self" is the class being instantiated. Often self = Dog, but inheritance
---    self = Dog, but inheritance can change it.
+--    can change it. newObj gets self's functions when we set both newObj's
---    newObj gets self's functions when we set both
+--    metatable and self's __index to self.
---    newObj's metatable and self's __index to self.
 -- 5. Reminder: setmetatable returns its first arg.
--- 6. The : works as in 2, but this time we expect
+-- 6. The : works as in 2, but this time we expect self to be an instance
---    self to be an instance instead of a class.
+--    instead of a class.
 -- 7. Same as Dog.new(Dog), so self = Dog in new().
 -- 8. Same as mrDog.makeSound(mrDog); self = mrDog.
 
-----------------------------------------------------
+--------------------------------------------------------------------------------
 
 -- Inheritance example:
 
@@ -315,17 +303,16 @@ end
 seymour = LoudDog:new()                       -- 3.
 seymour:makeSound()  -- 'woof woof woof'      -- 4.
 
+--------------------------------------------------------------------------------
 -- 1. LoudDog gets Dog's methods and variables.
 -- 2. self has a 'sound' key from new(), see 3.
--- 3. Same as LoudDog.new(LoudDog), and converted to
+-- 3. Same as "LoudDog.new(LoudDog)", and converted to "Dog.new(LoudDog)" as
---    Dog.new(LoudDog) as LoudDog has no 'new' key,
+--    LoudDog has no 'new' key, but does have "__index = Dog" on its metatable.
---    but does have __index = Dog on its metatable.
+--    Result: seymour's metatable is LoudDog, and "LoudDog.__index = Dog". So
---    Result: seymour's metatable is LoudDog, and
+--    seymour.key will equal seymour.key, LoudDog.key, Dog.key, whichever
---    LoudDog.__index = Dog. So seymour.key will
---    = seymour.key, LoudDog.key, Dog.key, whichever
 --    table is the first with the given key.
--- 4. The 'makeSound' key is found in LoudDog; this
+-- 4. The 'makeSound' key is found in LoudDog; this is the same as
---    is the same as LoudDog.makeSound(seymour).
+--    "LoudDog.makeSound(seymour)".
 
 -- If needed, a subclass's new() is like the base's:
 function LoudDog:new()
@@ -335,13 +322,13 @@ function LoudDog:new()
   return setmetatable(newObj, self)
 end
 
-----------------------------------------------------
+--------------------------------------------------------------------------------
 -- 4. Modules.
-----------------------------------------------------
+--------------------------------------------------------------------------------
 
 
---[[ I'm commenting out this section so the rest of
+--[[ I'm commenting out this section so the rest of this script remains
---   this script remains runnable.
+--   runnable.
 ```
 
 ```lua
@@ -367,8 +354,8 @@ local mod = require('mod')  -- Run the file mod.lua.
 local mod = (function ()
   <contents of mod.lua>
 end)()
--- It's like mod.lua is a function body, so that
+-- It's like mod.lua is a function body, so that locals inside mod.lua are
--- locals inside mod.lua are invisible outside it.
+-- invisible outside it.
 
 -- This works because mod here = M in mod.lua:
 mod.sayHello()  -- Says hello to Hrunkner.
@@ -376,8 +363,8 @@ mod.sayHello()  -- Says hello to Hrunkner.
 -- This is wrong; sayMyName only exists in mod.lua:
 mod.sayMyName()  -- error
 
--- require's return values are cached so a file is
+-- require's return values are cached so a file is run at most once, even when
--- run at most once, even when require'd many times.
+-- require'd many times.
 
 -- Suppose mod2.lua contains "print('Hi!')".
 local a = require('mod2')  -- Prints Hi!