= Lua
== String library functions (5.4)

> for k,v in pairs(string) do print(k) end
byte
char
dump
find         if you need the first match and its position
format
gmatch       if you are interested in matches and want to iterate over them
gsub         if you substitute the matches ignoring their position
match        if you need all captures from the first match
len
lower
pack
packsize
rep
reverse
sub
unpack
upper

{find, gmatch, gsub, match} need a Lua pattern as argument.

== Lua patterns

tutorial:       http://lua-users.org/wiki/PatternsTutorial
documentation:  https://www.lua.org/manual/5.3/manual.html#6.4.1

.        … matches a single character
%d %a %g … matches a single digit, letter, printable except space respectively
%l %s %w … matches a lowercase character, a whitespace, or an alphanumeric character respectively
%x       … matches a hexdecimal character
         … their definition is locale-dependent… [a-z] is not necessarily equivalent to %l
%C       … with C as any character not defined to be a character class: character C taken literally
[a-z]    … matches a character of the provided character class between braces
[^%l_]   … matches the complement of the provided character class %l and _, due to "^"

^PATTERN … requires the pattern to be at the start of the string
PATTERN$ … requires the pattern to be at the end of the string

X*        … 0–∞ repetitions, searches for longest match
X+        … 1–∞ repetitions
X-        … 0–∞ repetitions, searches for shortest match
X?        … 0–1 repetitions
(PATTERN) … match pattern with a capture
()        … a special capture which captures the current byte position

%N       … N ∈ {1, …, 9}, represents the content of the n-th capture
         … captures are enumerated by their opening-parenthesis from left to right (as common in regex)
%bAB     … "balancing pattern": A and B are two characters and a match finds balanced pairs
  ("aaafff"):find("%baf")       → returns (1, 6) = first & last character position
  ("aaaff"):find("%baf")        → returns (2, 5) = first & last character position of balanced characters
  ("aaaa"):find("%baa")         → returns (1, 2)
%f[set]  … "frontier pattern": matches empty string at position P such that P-1 is not in the provided set, but P is
  ("a test"):match("%f[%s].+")  → returns ` test`
  ("aaabaa"):find("%f[a]")      → returns 1, because the start of the string has state "not in provided set"

== metatable methods

https://gist.github.com/oatmealine/655c9e64599d0f0dd47687c1186de99f

__add(a, b)
__sub(a, b)
__mul(a, b)
__div(a, b)
__unm(a)
__mod(a, b)	Lua 5.1
__pow(a, b)	Lua 5.1
__idiv(a, b)	Lua 5.3

__band(a, b)	Lua 5.3
__bor(a, b)	Lua 5.3
__bxor(a, b)	Lua 5.3
__bnot(a)	Lua 5.3
__shl(a, b)	Lua 5.3
__shr(a)	Lua 5.3

__eq(a, b)
__lt(a, b)
__le(a, b)

__concat(a, b)
__len(a)	Lua 5.1

__index(self, k)
__newindex(self, key, value)
__call(args)
__mode
__close(value, err?)	Lua5.4
__gc()

__tostring()
__metatable
__name
__pairs

== iterators

-- example for an iterator
-- NOTE: if your iterator handles tables, you might be interested in “next_key, next_value = next(tbl, previous_key)” or “nextval“ functions
local steps = function (start, stop, step_by)
  local iter = start
  return function ()
    local current = iter
    if current < stop then
      iter = iter + (step_by or 1)
      return current
    else
      return nil
    end
  end
end

for i in steps(3, 7, 1) do
  print(i)
end